When I try to put a certain png file in the background of the toolbar, mirc crashes, poping a 'runtime error' messagebox. Here is the image that does this
I don't get a 404. On IE the image loads most of the way then goes to a red x. On NetScape (don't laugh) it loads most of the way then leaves the rest white.
I don't know what restrictions there are on filesizes on free webhosts at the moment but it could be that the image is too large to serve from there. You might want to split it into one image per screenshot.