It sounds to me like your neck is too thick for the capo. Most Shubb capos come with a little plastic piece on the end of the screw that keeps the screw from wearing a groove in the metal when the capo is closed. If you remove the little plastic piece, WALLA! You have a capo capable of accomodating a wider neck.
Of course, you might have tried that, in which case - I got nothin'.