Strange error with model icon file

I get this error:

suddenly when trying to use a model icon. The icon worked fine when it was still 30x30, but was cut off partially by the timers when they started. I resized it and now get this error.. which makes no sense whatsoever to me. Any ideas?

Edit: And just to make things even weirder, if I increase the image size to 30x30 with an invisible frame around it, it suddenly works fine again.