Well well well, it's good to see a bug I'm not in charge of :D
Me changing the thumbnail to a timely 144x144 pixel size should be of no consequence and is the advised thumbnail size.
Something in ur modlist mod is very rigid and unhappy about changes, you should talk with the other author.
But Iuckily I can just force the modlist mod to make a proper scan for this mod, so you can have a quick fix until that.