Probably you just have tried to login to Plesk and got the following message:
500 – Internal Server Error
The easiest way is to check the log file of Plesk:
# cat /var/log/sw-cp-server/error_log
If you couldn’t find any strange messages (except the SSL warnings, those are known) then you can try the following, it will probably show you the cause of the problem:
# /usr/bin/sw-engine-cgi -c /usr/local/psa/admin/conf/php.ini -d auto_prepend_file=auth.php3 -u psaadm
In my case the file system was in read-only mode and therefor Plesk was not working:
# /usr/bin/sw-engine-cgi -c /usr/local/psa/admin/conf/php.ini -d auto_prepend_file=auth.php3 -u psaadm
Could not open Repository at “/etc/sw/keys”: /etc/sw/keys/lock/repository: cannot create: Read-only file system
PHP Notice: Undefined index: REQUEST_URI in /opt/psa/admin/auto_prepend/auth.php3 on line 55
Status: 500 SWKeyExFatalError
Content-type: text/plain; charset=utf-8
Good luck with debugging Plesk!