Troubles uploading avatar

Ok, everytime I want to upload an avatar, there stands: Invalid File. What does that means? I do have the right size, so what else could be it?

Ok sorry, 10 seconds after starting this thread I found it out myself. I gave the wrong URL,
instead of http://img131.imageshack.us/img131/5...avatar2kz9.jpg
This thread can be closed, sorry for this

What Image type are you trying to upload? as your avatar?? There are restrictions on type of image you cannot have animatred image as avatr, or flash or movie.