Arm exercises aren't really necessary and have minimal gain for an experienced weight lifter (someone who's been lifting consistently for months on end, not someone who just knows a lot)
IF you're doing the big movements... if you aren't doing the big movements you will probably stop making gains indefinetly before soon. That being said do what you like and most certainly don't do something that HURTS you... even though most of us here like the pain, there's good and bad pain, and what you're describing does not sound good. If you really wanna do that exercise I recommend either lowering the weight and doing higher reps or getting in a better warm-up or stop doing them for a while and come back later.
Personally I like using cables and do the one-arm pushdown shown here...
http://www.exrx.net/WeightExercises/Triceps/CBOneArmPushdown.html
It's a smooth full movement and I love the feel of full extension in the tricep muscle. hmm I use to do skull crusher's as well (new place has only one bar and is used for EZ curls) ... didn't know they had such a cool name before.