I get this error
Upload warning
Files of the MIME type "application/x-php" are not allowed to be uploaded.
when I try to upload this image. I made that image the same way for everyone I uploaded already, but this particular one isn't accepted. Does anyone know why?
Just try saving the image again by copying the content and pasting onto a new window in your graphics editor. The wiki uploading thing just reads the image meta data without going further, so maybe just a saving glitch.