[kermit2]

vbulletin has it's own 'too busy' message, although I think it's something like 'forum too busy' - there's an option to control it in the ACP. Sounds like it isn't this though.

Sounds to me more like you're exceeding Apache's max clients. Try grepping for MaxClients in your Apache config file, then run:

ps aux|grep apache|wc -l

(may need to grep for httpd instead), to see how many clients it is currently serving. If the output of the above command is regularly getting close to your MaxClients, you could see about raising MaxClients. That's assuming your server can handle more clients.

You might want to see about lowering your KeepAliveTimeout a little too, if KeepAlive is turned on. That should result in each Apache process hanging around for less time after it has served the request(s), which will reduce the number of concurrent processes