I don't know if its just me but I had never had this problem before with any other forums.
The control panel of the icon section won't let me upload any icons from my computer.
One error was that it couldn't handle this format:
So I tried .jpg .png .gif but it still gave me that error.

Another time it said I can't have the dimension
Which I put 100x100

I think this control panel hates me

Hmm, I came across that problem, I got the same message but my avatar got uploaded

Try uploading it on Photobucket or Imgshack, then copy the Http code and paste it

I was having the same problem...Thnks ToxicStream i uploaded it Photobucket at copied the Http code and it worked