I don't think the dimensions can cause an error, but I got mine working a while ago (
http://puu.sh/kJJbw/a250ae0263.png) and has not had any problems since, so I know the function works.
If you want to see if the dimensions are a problem though, you can try 482x226, which is identical to the image I have in my template. If you want to try, try downloading this image (Right Click > Save Image As...) and change it to suit your mod. Make sure your LauncherPic in the entry.hpc matches your file name for your image.
![[Image: cea5524a10.png]](http://puu.sh/lamyc/cea5524a10.png) 
If it still doesn't work, pack up your Campaign and upload it to a service like Dropbox or Mediafire and I'll take a look and see if I can find the issue.