[Users] Mysql connection timeout issue

Hi to all, i'm experiencing strange behavior and want to ask a clue. After some time of inactivity (around 15 hour more or less) or few activity on my Openser i start getting message in my logs:

submit_query: MySQL server has gone away db_query: Error while submitting query is_local(): Error while querying database

and obviously openser is no more working. I have to restart openser to have reopened the connection. I'm using mysql 5.0.15-max and was thinking on the wait_timeout or interactive_timeout variables in mysql that by default are at 28800 (8 hour). I raised both variables to 1000000 but still getting the problem. Did you have any ideas? Thanks, Bye, Marcello