So then your using the exact same database? (ie your OSTicket tables are in the same database as your joomla tables.) Because if not then you will need to setup permissions on the mysql user for the new database.
example:
MySQL server: myserver.domain.com
database: Joomla
tables: all joomla tables, all osticket tables
While this is fine you definitely should utilize the default ost_ prefix.
This setup allows you to utilize one username/password and set of permissions.
If you are set up like I am it would look more like:
MySQL server: myserver.domain.com
database: Joomla
tables: all joomla tables
database: osticket
tables: all osticket tables
This setup allows you to utilize one username/password but requires two sets of permissions.
note: I always utilize one username/password per database. I also do not mix my usernames access between products. If I am running say Drupal, Osticket, and PHPBB then I will have three separate database names, usernames, passwords, and permissions for just their database. I personally do this because like to segregate my products. If I decide to migrate to say Joomla or Wordpress I can simply drop the drupal database rather then have to write a query to drop all the tables beginning with say the drupal_ prefix. Also if I want to only back up/restore a specific set of tables its trivial and the backup files are much smaller and more manageable. Please realize that this is subjective and opinionated. You are free to set your stuff up however you want if it works for you.