Lots of people get cramps when they start low-carb eating, and magnesium supplements helps relieve the cramps. So changing from high-carb to low carb can cause cramps.

I have noticed a "flip-flop" effect of cramps, though. If I partake of a treat (I'm on maintenance) that is high carb I will suffer leg cramps. So I get leg cramps when I switch from low to high carbs. Magnesium also helps this. (In fact, I don't eat treats very often because of the cramp factor - they just aren't worth it.)

I have not yet figured out the chemistry behind the cramps both when going from high to low and from low to high carbs.
Anyway, magnesium should help, and maybe potassium also. I believe calcium also plays a part in cramping.