I am using Minecraft 1.6 and Forge 1.6. I do not have a launcher and I am not using a patcher. When the mods folder is empty, all is harmony in Minecraft, but whenever I put a mod in (I have tested with five mods, all of which the creators say work with Forge) I get a classnotfoundexception error.
Here is a Minecraft error test log: http://pastebin.com/tPe5b7LL
Here is Minecraft's own crash report: http://pastebin.com/Z2eHrzfr
Here is the Forge crash log: http://pastebin.com/MhvQBif5
I've tried reinstalling Forge, redownloading the mods, contacting the mod owners (they don't understand), updating Minecraft, deleting minecraft.jar, and crying helplessly and none of them have worked. I'm sorry if the solution is obvious but I am seriously confused.