Oh, it's hard to say exactly, there were a lot of changes since last time

I've added one new feature to xupload.js called "Normalized file fields naming". This works when you add e.g. 3 files, then delete 2nd one and your slots will be named not file_0,file_2 (could be the problem if in your PHP script you check for upload fields in cycle), but file_0,file_1. Well...if this feature is not important for you, you can skip updating xupload.js file.
Anyway, check everything under Mac.