8
Ok, I know why this is happening to you guys. When you get the error stating that you're trying to upload an image that is to large or the size is incorrect, well, instead of hitting the back button re click on the 'Edit account' in the user menu and start again. I know :/
The issue is that XOOPS checks that the form is valid and when you click on the back button basically XOOPS thinks you are trying to resend the information and invalidates the 'token'.
I will fix this and submit it to svn later.