This can be because...
The silicone coating on the threads in the device has been removed. There is a silicone coating on the threads of the CryoPen® devices. This MUST NOT be removed. It makes piercing the cartridge impossible if removed. This coating may be accidentally removed by someone cleaning the device in-between treatments. You can purchase a silicone lubricant to re-apply to the threads (Halfords Silicone Spray)