It returns a javascript alert() filled with the current pages html (seems very odd that could happen)
I can browse to the url (http://thegootgame.com/submit-a-picture/handleswfupload), and the function is loaded fine as I can echo out a string.
In the debug window i can see this:
SWF DEBUG: Event: uploadSuccess: File ID: SWFUpload_0_0 Data: <!DOCTYPE html>
and the entire html follows on from there