The technical explanation isn't much different. Server hiccups. MySQL glitches. Xmsn errors. Power dips. Flaky RAM. Disk errors....
There would have to be quite a few of them -- I've been seeing it almost daily.
A "page refresh" may yield the (apparent) result of clearing the error, but it doesn't have much to do with the underlying problem(s).
I know, I just had to take the Microsoft way(where restarting makes problems go away, but then refresh here), as there's not much I could do at the moment.
confess( "I offer no guarantees on my code." );