Sorry, been away so only just read your reply.
The usual problem is that unlike all other programmers, I don't write perfect code every time and during dev. I occasionally create an endless loop. It only takes one of these for the server to throw it's toys out of the pram. I thought there may be a setting somewhere on the server to limit the time a script can run.
Not having a time limit is useful sometimes but can also come back to bite you.