Do you mean /var/lib/roundcube/logs/errors?
It say
[10-Aug-2013 00:28:28 +0200]: IMAP Error: Login failed for myemail from myip. AUTHENTICATE PLAIN: Authentication failed. in /var/lib/roundcube/program/lib/R
[10-Aug-2013 00:25:43 +0200]: SMTP Error: SMTP error: Failed to add recipient 'myemail' in /var/lib/roundcube/program/include/rcmail.php on line 1014 (POST /webmail/?_unlock=loading1376087141354&_lang=en?_task=mail&_action=send)
But these logs are from today, there is no logs from tomorrow, these errors isnt related to my
ERROR 500 - Internal Server Error!
The following error occurred:
The requested URL caused an internal server error.
If you get this message repeatedly please contact the webmaster.
is it? Where can I find that??
This is very weird, I tried to enable the installer again, and I get the same error on the /installer site