if you have Nero you can Open the MP4-AAC file in Nero Wave Editor and do a "Save As" whatever audio format you want (including MP3/mp3Pro).

or try http://www.dbpoweramp.com/
http://www.softe.net

or

Open Nero Burning ROM (not Nero Express)
2. go to Extras>Encode Files
3. Click in Add and select your audio files
4. in output file format select de codec you want
5. in target directory browse to a folder of your preference and click go


if all else fails. Find a diffrent beat to use. lol.
hope that helps.