What causes this to fail?

You are in a better position to determine this than we are because you probably know what was reported for $! while we do not. Perhaps you'd get better results if you shared that information.

Normally I'd also make a wild guess, but in this case, lacking that item, all of the guesses just seem too wild ($socket has been closed, ...).

Usually I wouldn't post this response but it has been days and you haven't gotten an answer to this part of your question.

                - tye