Check this thread if you haven't already:
showthread.php?t=24450
I had the same problem and appearently I was missing files in my SA installation folder. I got help from support fixing this issue. Im not positive you're problem is the same and I can't help you with the files but Im sure WA Support will help you fix this! Now you have a clue at least what the problem can be!
Regards,
Martin J.