I assume the mod is not supposed to be in the server mods folder, as it works just fine in client. I'm used to throwing all my 50~ mods in the server folder not caring whether they're client side only or server side too, because it'd be too tedious to sort.

Could a check be added to allow having the .jar file in the server mods folder?

http://pastebin.com/JpkAeyRN

This was a mistake I made when I was fixing issue #4
It will be fixed in next release.