Unfortunately I cannot provide any insight into your cramping experience, but the Presses I can comment on.
First, you need to wear your belt tighter. It seemed to actually slip down as the set went on.
Second, you need to unrack the bar with vertical forearms and straight wrists and keep them that way throughout the set. Do not let your elbows dip in between reps, keep them up higher than you think they need to be