Are you installing modloader/TMI/MoreCreeps into your .jar? Go into .minecraft, then versions then find your B1.7.3 folder, find the .jar install the mods there.
So I was making a modpack for myself to play within MultiMC and everything loads up just fine, until I create a world. The MultiMC log is below. If I need to get rid of a mod I'll probably do that. If I posted this in the wrong location, sorry about that, I don't know where to post this, but feel free to move it to the correct location. Thanks.
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Click me for MultiMC Log