I've got exactly the same problem. I'm using XP Pro on a i815 motherboard and USB is really flakey. It does occasionally work but normally I just get that error message.

If I tell emplode to create a log then in there it complains about some sequence number not being what it expects.

I haven't played about with it much though because I just use ethernet now to upload and it's much more reliable. I do occasionally get an error message but I try again it works.

- Trevor