A Caching Plugin? Can you ask them to be more specific? I don't know that I have ever heard of one.
I have heard of that error. That is a server issue and you would need to contact your hosting provider and request them to increase the value for your mysql setting: max_allowed_packet. However, it sounds like they aren't will to do this for you.
You can see more about the error in the manual here -
http://www.vbulletin.com/docs/html/t...t_mysql_errors
There is this article - perhaps this is what your host is thinking of -
Work Around: Error SQL server exceeded max questions