It's the file structure. If you take your time and look closely at where the files have been placed, I am sure you will find a mistake in the way it placed the files. Problems can occur sometimes when the modder places files in strange places, and often, you can work it out by comparing your original track files with the converted files. I have had times when I had to unpack the mas file to find where the error was. I would also point out that whichever track it is you are trying to convert is most likely already available somewhere.