I started with 1.1.1 and upgraded to 1.1.4...the following issue occurs on both releases. Others have posted parts of this, without any resolution.
The default configuration enables a pair of plugins, though I believe the problem occurs for other enabled plugins. Seems config.inc.php cannot be found by rcube_plugin.php. I'm wondering if traversing two symbolic links is causing a problem for rcube_plugin.php? ('archive' has no configuration file which might explain the problem.)
General case for the errors found in /var/log/roundcube/errors:
[04-Jan-2016 09:20:00 -0800]: <amukbv7a> PHP Error: Failed to load config from /var/lib/roundcube/plugins/zipdownload/config.inc.php in /usr/share/roundcube/program/lib/Roundcube/rcube_plugin.php on line 157 (POST /webmail/?_task=mail&_action=refresh?_task=&_action=)
[04-Jan-2016 09:20:04 -0800]: <amukbv7a> PHP Error: Failed to load config from /var/lib/roundcube/plugins/jqueryui/config.inc.php in /usr/share/roundcube/program/lib/Roundcube/rcube_plugin.php on line 157 (GET /webmail/?_task=logout&_token=545fbdfa591c8cf4b775c662d141af4f)
for enabled plugins:
$config['plugins'] = array(
'archive',
'zipdownload',
);
ls -l /etc/roundcube/plugins/
total 68
drwxr-xr-x 2 root root 4096 Nov 24 10:55 acl
drwxr-xr-x 2 root root 4096 Nov 24 10:55 additional_message_headers
drwxr-xr-x 2 root root 4096 Nov 24 10:55 compose_addressbook
drwxr-xr-x 2 root root 4096 Nov 24 10:55 database_attachments
drwxr-xr-x 2 root root 4096 Nov 24 10:55 dovecot_impersonate
drwxr-xr-x 2 root root 4096 Nov 24 10:55 help
drwxr-xr-x 2 root root 4096 Nov 24 10:55 http_authentication
drwxr-xr-x 2 root root 4096 Nov 24 10:55 jqueryui
drwxr-xr-x 2 root root 4096 Nov 24 10:55 managesieve
drwxr-xr-x 2 root root 4096 Nov 24 10:55 markasjunk2
drwxr-xr-x 2 root root 4096 Nov 24 10:55 newmail_notifier
drwxr-xr-x 2 root root 4096 Nov 24 10:55 new_user_identity
drwxr-xr-x 2 root root 4096 Nov 24 10:55 password
drwxr-xr-x 2 root root 4096 Nov 24 10:55 sauserprefs
drwxr-xr-x 2 root root 4096 Nov 24 10:55 sieverules
drwxr-xr-x 2 root root 4096 Nov 24 10:55 squirrelmail_usercopy
drwxr-xr-x 2 root root 4096 Nov 24 10:55 zipdownload
ls -l /usr/share/roundcube/plugins/
total 184
drwxr-xr-x 5 root root 4096 Jan 4 08:39 acl
drwxr-xr-x 3 root root 4096 Jan 4 08:39 additional_message_headers
drwxr-xr-x 5 root root 4096 Jan 4 08:39 archive
drwxr-xr-x 3 root root 4096 Jan 4 08:39 attachment_reminder
drwxr-xr-x 3 root root 4096 Jan 4 08:39 autologon
drwxr-xr-x 4 root root 4096 Nov 24 10:55 compose_addressbook
drwxr-xr-x 4 root root 4096 Nov 24 10:55 contextmenu
drwxr-xr-x 3 root root 4096 Nov 24 10:55 copymessage
drwxr-xr-x 3 root root 4096 Jan 4 08:39 database_attachments
drwxr-xr-x 4 root root 4096 Jan 4 08:39 debug_logger
drwxr-xr-x 4 root root 4096 Nov 24 10:55 dkimstatus
drwxr-xr-x 2 root root 4096 Nov 24 10:55 dovecot_impersonate
drwxr-xr-x 3 root root 4096 Jan 4 08:39 emoticons
drwxr-xr-x 7 root root 4096 Jan 4 08:39 enigma
drwxr-xr-x 3 root root 4096 Jan 4 08:39 example_addressbook
drwxr-xr-x 2 root root 4096 Nov 24 10:55 fail2ban
drwxr-xr-x 3 root root 4096 Jan 4 08:39 filesystem_attachments
drwxr-xr-x 6 root root 4096 Jan 4 08:39 help
drwxr-xr-x 5 root root 4096 Jan 4 08:39 hide_blockquote
drwxr-xr-x 3 root root 4096 Jan 4 08:39 http_authentication
drwxr-xr-x 3 root root 4096 Jan 4 08:39 identity_select
drwxr-xr-x 5 root root 4096 Jan 4 08:39 jqueryui
drwxr-xr-x 4 root root 4096 Nov 24 10:55 keyboard_shortcuts
drwxr-xr-x 5 root root 4096 Jan 4 08:39 legacy_browser
drwxr-xr-x 3 root root 4096 Nov 24 10:55 listcommands
drwxr-xr-x 6 root root 4096 Jan 4 08:39 managesieve
drwxr-xr-x 5 root root 4096 Jan 4 08:39 markasjunk
drwxr-xr-x 5 root root 4096 Nov 24 10:55 markasjunk2
drwxr-xr-x 4 root root 4096 Nov 24 10:55 message_highlight
drwxr-xr-x 4 root root 4096 Jan 4 08:39 newmail_notifier
drwxr-xr-x 4 root root 4096 Jan 4 08:39 new_user_dialog
drwxr-xr-x 3 root root 4096 Jan 4 08:39 new_user_identity
drwxr-xr-x 6 root root 4096 Jan 4 08:39 password
drwxr-xr-x 4 root root 4096 Nov 24 10:55 quickrules
drwxr-xr-x 3 root root 4096 Jan 4 08:39 redundant_attachments
drwxr-xr-x 5 root root 4096 Nov 24 10:55 sauserprefs
drwxr-xr-x 3 root root 4096 Jan 4 08:39 show_additional_headers
drwxr-xr-x 7 root root 4096 Nov 24 10:55 sieverules
drwxr-xr-x 3 root root 4096 Jan 4 08:39 squirrelmail_usercopy
drwxr-xr-x 4 root root 4096 Jan 4 08:39 subscriptions_option
drwxr-xr-x 4 root root 4096 Nov 24 10:55 thunderbird_labels
drwxr-xr-x 4 root root 4096 Jan 4 08:39 userinfo
drwxr-xr-x 5 root root 4096 Jan 4 08:39 vcard_attachments
drwxr-xr-x 3 root root 4096 Jan 4 08:39 virtuser_file
drwxr-xr-x 3 root root 4096 Jan 4 08:39 virtuser_query
drwxr-xr-x 5 root root 4096 Dec 23 01:17 zipdownload
ll /var/lib/roundcube/plugins/
total 8
drwxr-xr-x 2 root root 4096 Nov 24 10:55 ./
drwxr-xr-x 6 root root 4096 Jan 4 10:32 ../
lrwxrwxrwx 1 root root 32 May 6 2015 acl -> /usr/share/roundcube/plugins/acl/
lrwxrwxrwx 1 root root 55 May 6 2015 additional_message_headers -> /usr/share/roundcube/plugins/additional_message_headers/
lrwxrwxrwx 1 root root 36 May 6 2015 archive -> /usr/share/roundcube/plugins/archive/
lrwxrwxrwx 1 root root 38 May 6 2015 autologon -> /usr/share/roundcube/plugins/autologon/
lrwxrwxrwx 1 root root 48 Oct 22 2013 compose_addressbook -> /usr/share/roundcube/plugins/compose_addressbook/
lrwxrwxrwx 1 root root 40 Oct 22 2013 contextmenu -> /usr/share/roundcube/plugins/contextmenu/
lrwxrwxrwx 1 root root 40 Oct 22 2013 copymessage -> /usr/share/roundcube/plugins/copymessage/
lrwxrwxrwx 1 root root 49 May 6 2015 database_attachments -> /usr/share/roundcube/plugins/database_attachments/
lrwxrwxrwx 1 root root 41 May 6 2015 debug_logger -> /usr/share/roundcube/plugins/debug_logger/
lrwxrwxrwx 1 root root 39 Oct 22 2013 dkimstatus -> /usr/share/roundcube/plugins/dkimstatus/
lrwxrwxrwx 1 root root 48 Oct 22 2013 dovecot_impersonate -> /usr/share/roundcube/plugins/dovecot_impersonate/
lrwxrwxrwx 1 root root 38 May 6 2015 emoticons -> /usr/share/roundcube/plugins/emoticons/
lrwxrwxrwx 1 root root 37 Oct 22 2013 fail2ban -> /usr/share/roundcube/plugins/fail2ban/
lrwxrwxrwx 1 root root 51 May 6 2015 filesystem_attachments -> /usr/share/roundcube/plugins/filesystem_attachments/
lrwxrwxrwx 1 root root 33 May 6 2015 help -> /usr/share/roundcube/plugins/help/
lrwxrwxrwx 1 root root 44 May 6 2015 hide_blockquote -> /usr/share/roundcube/plugins/hide_blockquote/
lrwxrwxrwx 1 root root 48 May 6 2015 http_authentication -> /usr/share/roundcube/plugins/http_authentication/
lrwxrwxrwx 1 root root 37 May 6 2015 jqueryui -> /usr/share/roundcube/plugins/jqueryui/
lrwxrwxrwx 1 root root 47 Oct 22 2013 keyboard_shortcuts -> /usr/share/roundcube/plugins/keyboard_shortcuts/
lrwxrwxrwx 1 root root 41 Oct 22 2013 listcommands -> /usr/share/roundcube/plugins/listcommands/
lrwxrwxrwx 1 root root 40 May 6 2015 managesieve -> /usr/share/roundcube/plugins/managesieve/
lrwxrwxrwx 1 root root 39 May 6 2015 markasjunk -> /usr/share/roundcube/plugins/markasjunk/
lrwxrwxrwx 1 root root 40 Oct 22 2013 markasjunk2 -> /usr/share/roundcube/plugins/markasjunk2/
lrwxrwxrwx 1 root root 46 Oct 22 2013 message_highlight -> /usr/share/roundcube/plugins/message_highlight/
lrwxrwxrwx 1 root root 45 May 6 2015 newmail_notifier -> /usr/share/roundcube/plugins/newmail_notifier/
lrwxrwxrwx 1 root root 44 May 6 2015 new_user_dialog -> /usr/share/roundcube/plugins/new_user_dialog/
lrwxrwxrwx 1 root root 46 May 6 2015 new_user_identity -> /usr/share/roundcube/plugins/new_user_identity/
lrwxrwxrwx 1 root root 37 May 6 2015 password -> /usr/share/roundcube/plugins/password/
lrwxrwxrwx 1 root root 39 Oct 22 2013 quickrules -> /usr/share/roundcube/plugins/quickrules/
lrwxrwxrwx 1 root root 40 Oct 22 2013 sauserprefs -> /usr/share/roundcube/plugins/sauserprefs/
lrwxrwxrwx 1 root root 52 May 6 2015 show_additional_headers -> /usr/share/roundcube/plugins/show_additional_headers/
lrwxrwxrwx 1 root root 39 Oct 22 2013 sieverules -> /usr/share/roundcube/plugins/sieverules/
lrwxrwxrwx 1 root root 50 May 6 2015 squirrelmail_usercopy -> /usr/share/roundcube/plugins/squirrelmail_usercopy/
lrwxrwxrwx 1 root root 49 May 6 2015 subscriptions_option -> /usr/share/roundcube/plugins/subscriptions_option/
lrwxrwxrwx 1 root root 47 Oct 22 2013 thunderbird_labels -> /usr/share/roundcube/plugins/thunderbird_labels/
lrwxrwxrwx 1 root root 37 May 6 2015 userinfo -> /usr/share/roundcube/plugins/userinfo/
lrwxrwxrwx 1 root root 46 May 6 2015 vcard_attachments -> /usr/share/roundcube/plugins/vcard_attachments/
lrwxrwxrwx 1 root root 42 May 6 2015 virtuser_file -> /usr/share/roundcube/plugins/virtuser_file/
lrwxrwxrwx 1 root root 43 May 6 2015 virtuser_query -> /usr/share/roundcube/plugins/virtuser_query/
lrwxrwxrwx 1 root root 40 May 6 2015 zipdownload -> /usr/share/roundcube/plugins/zipdownload/
ll /usr/share/roundcube/plugins/*/config.inc.php
lrwxrwxrwx 1 root root 41 May 6 2015 /usr/share/roundcube/plugins/acl/config.inc.php -> /etc/roundcube/plugins/acl/config.inc.php
lrwxrwxrwx 1 root root 64 May 6 2015 /usr/share/roundcube/plugins/additional_message_headers/config.inc.php -> /etc/roundcube/plugins/additional_message_headers/config.inc.php
lrwxrwxrwx 1 root root 57 Oct 22 2013 /usr/share/roundcube/plugins/compose_addressbook/config.inc.php -> /etc/roundcube/plugins/compose_addressbook/config.inc.php
lrwxrwxrwx 1 root root 58 May 6 2015 /usr/share/roundcube/plugins/database_attachments/config.inc.php -> /etc/roundcube/plugins/database_attachments/config.inc.php
lrwxrwxrwx 1 root root 57 Oct 22 2013 /usr/share/roundcube/plugins/dovecot_impersonate/config.inc.php -> /etc/roundcube/plugins/dovecot_impersonate/config.inc.php
lrwxrwxrwx 1 root root 42 May 6 2015 /usr/share/roundcube/plugins/help/config.inc.php -> /etc/roundcube/plugins/help/config.inc.php
lrwxrwxrwx 1 root root 57 May 6 2015 /usr/share/roundcube/plugins/http_authentication/config.inc.php -> /etc/roundcube/plugins/http_authentication/config.inc.php
lrwxrwxrwx 1 root root 46 May 6 2015 /usr/share/roundcube/plugins/jqueryui/config.inc.php -> /etc/roundcube/plugins/jqueryui/config.inc.php
-rw-r--r-- 1 root root 137 Apr 10 2013 /usr/share/roundcube/plugins/keyboard_shortcuts/config.inc.php
lrwxrwxrwx 1 root root 49 May 6 2015 /usr/share/roundcube/plugins/managesieve/config.inc.php -> /etc/roundcube/plugins/managesieve/config.inc.php
lrwxrwxrwx 1 root root 49 Oct 22 2013 /usr/share/roundcube/plugins/markasjunk2/config.inc.php -> /etc/roundcube/plugins/markasjunk2/config.inc.php
lrwxrwxrwx 1 root root 54 May 6 2015 /usr/share/roundcube/plugins/newmail_notifier/config.inc.php -> /etc/roundcube/plugins/newmail_notifier/config.inc.php
lrwxrwxrwx 1 root root 55 May 6 2015 /usr/share/roundcube/plugins/new_user_identity/config.inc.php -> /etc/roundcube/plugins/new_user_identity/config.inc.php
lrwxrwxrwx 1 root root 46 May 6 2015 /usr/share/roundcube/plugins/password/config.inc.php -> /etc/roundcube/plugins/password/config.inc.php
lrwxrwxrwx 1 root root 49 Oct 22 2013 /usr/share/roundcube/plugins/sauserprefs/config.inc.php -> /etc/roundcube/plugins/sauserprefs/config.inc.php
lrwxrwxrwx 1 root root 48 Oct 22 2013 /usr/share/roundcube/plugins/sieverules/config.inc.php -> /etc/roundcube/plugins/sieverules/config.inc.php
lrwxrwxrwx 1 root root 59 May 6 2015 /usr/share/roundcube/plugins/squirrelmail_usercopy/config.inc.php -> /etc/roundcube/plugins/squirrelmail_usercopy/config.inc.php
lrwxrwxrwx 1 root root 49 May 6 2015 /usr/share/roundcube/plugins/zipdownload/config.inc.php -> /etc/roundcube/plugins/zipdownload/config.inc.php
