Apparently you have a bad skin.. if you can not determine which one it is you
will need to start deleting them until the error goes away or till you just have
OFFicial skins left.
Click on Skin, select and remove.
OR
 Try going in the back door! LOL
shut your IM Down completely
Here is where mine are:
C:\Program Files\IncrediMail\Data\Skin
Delete them from there!
You may need to reboot.. then open IM again