Dev Launcher cannot launch renamed (possilby modded) .jar files.

After the update to 0.9.2 the Dev Launcher is giving an error and fails to launch any renamed .jars. I have a 1.5.1 jar modded to play The Aether mod, renamed and placed in another folder (along with modified/renamed .json) and any time I try to launch it I get this bit of code.

Getting syncinfo for selected version
Queueing library & version downloads
Download job 'Version & Libraries' started (8 threads, 1 files)
Finished downloading C:\Users\Josh\AppData\Roaming\.minecraft\versions\1.5.1-Mod\1.5.1-Mod.jar for job 'Version & Libraries': Couldn't connect to server (responded with 403) but have local file, assuming it's good
Job 'Version & Libraries' finished successfully
Launching game
Unpacking natives to C:\Users\Josh\AppData\Roaming\.minecraft\versions\1.5.1-Mod\1.5.1-Mod-natives-2289352866663
Launching in C:\Users\Josh\AppData\Roaming\.minecraft
Can't run version, missing minecraftArguments
Deleting C:\Users\Josh\AppData\Roaming\.minecraft\versions\1.5.1-Mod\1.5.1-Mod-natives-2289352866663

Everything worked just fine yesterday, I haven't done anything to the files, and trying to make a new modded .jar wont work either.