Throwing in a me too...
It only happens once in a great while and we can't consistently reproduce the issue.
Using WebLogic 10.2
We just switched to Apache from IIS, I'm almost positive we never got this with IIS but we had other issues with IIS which is why we're switching to Apache.
Similar circumstances to Rick...we have a name search field and if you keep hammering on it it will sometimes throw the error.
The server is not clustered but we do have a BigIP in front of it for load balancing, right now there's only one server.