What, you just need to upload a mp3 to them? what's the problem then ? Are you trying to upload a wav track?
edit: sorry for being arrogant... i guess you don't know how to convert wav (the usual production software output format) to mp3 (the web music format)? What sequencer you are using?
na its not wav. its a fully rendered mp3 file but reverb is still askin for a mpeg or mp3 extension i cant remeber which.
i jus dont know what this extension is
its most likely the wrong file type.... wav/wma/aiff etc
if your sure its an mp3, maybe you have deleted the extension when renaming it....
for example, the file you upload should be called "tracknamehere.mp3" and not "tracknamehere"
if it has no extension its a simple matter of renaming... just make sure you type .mp3 at the end
Right if you burn an audio CD, the normal kind that you can listen to with your car stereo etc, it's not an mp3/wav/aiff but its cd audio format.