Best answer by Mathis
I've looked into this and the same root cause applies to all three of you - in order to upload, you have to have a valid email address registered to your account. The good news is: this should be an easy fix :)
Just head over to https://soundcloud.com/settings and add an email address. (Check your inbox afterwards to confirm / verify the email address as well). Once you've verified the email address, uploading should work just fine.
Sorry about the confusion, but I hope this sorts out things for you.