stripped screws
there are a few things you could try.
this frist i heard of recently of the internet, simple locktight your allne key into the scew, let it sit long enough for it to harden all the way and thentry and uncrew it. just pull the 2 apart when done and clean the locktight off the allen key
the second if the quick dirty way, cut the head off the screw (careful not to mar up your frame) and then pull the grip off and use some kind of wrench to grab onto the threads and unscrew it.
-TC