using the import manager, import a 256x256 tga file called "war3mapPreview.tga" and then right-click and select modify file properties, and delete the custom path (so you will basically see only the name of the file there and nothing else)
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.