grease the threads too. i know when i've put on pedals (even new pedals into new cranks) sometimes i feel the first few threads go, then it simply "stops" like you described. usually you just have to unscrew, then try screwing again. seems like if the pedal isn't going in the hole on the crank at the exact right angle, those threads just jam up a bit. obviously forcing wont help, just back off and re-attempt. also, yeah, as mentioned above, have threads checked out and cleaned up a bit if they look a bit burry. assuming this is going on that somec you got? pics pics pics.