Upgrade to ejabberd 16.06
Ejabberd upgrade process
One data type must be changed on the users table. This can be done at any time while ejabberd 16.04 is running. If you run an older version of ejabberd you must follow database upgrade process for 16.03 and 16.04 first.
Note: this applies only to MySQL. Other backend does not need upgrade.
MySQL database upgrade
mysql -h host -u user database -p << EOF ALTER TABLE muc_room MODIFY opts mediumtext NOT NULL; EOF