Fuze AVI MP4 problem

Im having a bit of an odd problem in that, i have two almost identical video files, and only one will work.

I downloaded two videos, then converted them both to MP4. i then popped them in SMC, and once fully completed, unplugged out my Fuze.Then went to videos, and checked on both, one worked fine, but the other came up with a red error message saying ‘this file format isn’t supported’ or something to that extent, and then it didn’t work. Im am confused as to why it wont work. It says something about the file format being AVI an being unsupported, but both files are MP4, both say MP4 on my computer and both have been under exactly the same conversions, downloaded from the same source, converted in the same program, both in SMC. what is going on?