[noname219]

So... hmm, I give up. After 2h30 of researching what was the problem, I just can't find it.
At first I thought it was Java that wasn't up to date, but after uninstalling/reinstalling everything Java touches, it didn't work.
Thought also it was the .jar file association that was causing troubles, everything looked fine, downloaded jarfix just to make sure, didn't work either.
Tried running another executable .jar file (a Minecraft version), it worked fine.

I really can't fix the problem myself. I'm running on Windows 7 x64 btw, if that helps.
As I said before, it worked with my Mac, so it may be a compatibility problem with my OS.