Get this error trying to access RoundCube Webmail after transferring to another server :
SERVICE CURRENTLY NOT AVAILABLE!
Error No. 
This indicate in most case something went wrong with the MySQL database transfer. Either you forgot to transfer the database on the new server or something definitely went wrong importing it. Start over the importation, it should work.
If you are using “mysqldump” utility to achieve this task, make sure using the following command to lock the DB during the exportation to avoid any data loss :
mysqldump -u USER -p --lock-all-tables DB_NAME > roundcube.sql