Roundcube error :: SERVICE CURRENTLY NOT AVAILABLE! Error No. 
I dealt with one of the following problem.
SERVICE CURRENTLY NOT AVAILABLE!
Error No. 
This problem occurs because of roundcube database structure has not updated properly.
There is a very simple command to resolve the issue
1) Login to the server as root
2) Just place the following command on a cPanel installed server.
[root@server~]# /usr/local/cpanel/bin/update-roundcube-sqlite –force
This will update the round cube forcefully on the server. This should now resolve the issue