There's a good chance mIRC has a maximum buffer size for loading images. This would not be a bug, just a limitation. I'd question why you would try to load such an image to begin with. If you really need to use such a large image in mIRC, you'll have to split up the file into smaller images and load it piece by piece. Given that it looks like you're scaling it, I'd suggest scaling it to the right size *before* loading it in mIRC.