This error pops up every now and then. I think it comes from too many people accessing the database at the same time. Supposedly this site can handle 100 connections at once. That means 100 people can access the database at the exact same time. Once you're done accessing, your connection is reset and it waits for the next person. This happens within milliseconds, usually.
I think what happens sometimes is, for one reason or another, the software doesn't let go of the connection to the database, even though you're not using it presently. For example, when you click on a thread, you access the database in order to retrieve that thread, but while you're reading it, your connection should be terminated since it'll probably take you a bit of time to read the whole thread.
Does this make any sense?