MIDI to MP3 Files Playing Too Fast

[Hybrinoid]

I'm aware there's already a thread for converting MIDI files to MP3, but that's not what I'm having problems with--I can get the files converted fine. However, when I play the new files, their speed (pitch, tempo, everything) is ludicrously fast. For example, a file that was 2:30 long when it was a MIDI came out as an MP3 that was 1:07 long, and playing it back in Audacity revealed what the problem was.

Anyone else having this problem, or know how to fix it? I'm using the newest version of Winamp.