Unable to login into my email account from Roundcube or Microsoft Outlook

Hello Guys,

Please help me. I am unable to login into my any email accounts across all user accounts.
I have just upgraded my server and since then I am unable to login into any of the email accounts.

Please can you help me how to identify the problem ?
Which logs can I check?

The error in the roundcube log is this line

AUTHENTICATE PLAIN: Inteal error occurred. Refer to server log for more information
 in /var/www/html/roundcubemail-1.3.3/program/lib/Roundcube/rcube_imap.php on line 196

Any tips. Please help