@djmind: I'm a bit fussy/pedantic/anal when it comes to Divx conversions, NVE's bar is too low.
@fritzi93: I've tried multiplex, I get the same error merging the streams.
@aldaco12: I'm pretty sure the files are ok, I've tried a couple of conversions with Divx files I've already done, and ones I've created myself, tried audio decompression, but still the same problem.
Thanks for your input guys, this weekend I'm formatting to make way for Win XP Pro, so I'll worry about it then. If something springs to mind though, please post it.