I don't know whether you guys fixed this in the latest SVN version but with the latest nightly shot downloaded from
Roundcube - Nightly Builds I run into trouble:
I got a lot of "Server Error (OK)" in beta 4 and that's why I upgraded to the nightly release. I was not able to load any mail in any of the IMAP folders.
$rcmail_config['debug_level'] is set to 13 per default in beta 4.
In the nightly shot i didn't get any "Server Error (OK)" but after the installation of the password plugin it complained again about that error.
Finally I found out that I had changed
$rcmail_config['debug_level'] = 1;
to
$rcmail_config['debug_level'] = 13;
for debugging reasons.
This is the reason for the "Server Error (OK)" bug! Just change it back to $rcmail_config['debug_level'] = 1; and it works like a charm.
I don't know whether this happens only to me, but this might be helping other users to make this app work.
All the best
Mario