What type of image, JPG, GIF or PNG?
Whats the file size of the image?
What is your server's php.ini (Control Panel > PHP Info) setting for post_max_size and upload_max_filesize?
Does your file's size exceed that limit?
UBB.threads doesnt really care about the width/height of an image. The image is processed by your server's GD/ImageMagik before stored as a post attachment. But if the image file size is too large (php.ini settings), it wont even be accepted by your server for processing.
