This can be due to a problem in the wiring or the auxiliary plug. To test either one, run your fingers along the wire and see if the problem can be temporarily fixed. If it can be fixed, the problem is with the wire and you will have to fix the wiring. For help with fixing the wiring, read the Skullcandy UPROCK Earpiece Wiring Replacement Guide.
If your fingers cannot grip the cushions, try using tweezers to grip the cushions and use your hands to keep them in place. For further assistance, visit the Skullcandy UPROCK Earpiece Cushions Replacement Guide.