I'm using a Spro and my pen functions very erratically. It will work for a minute and then quit for 5 seconds and then work for 10 seconds and quit for 2 and then work for 3 and quit for 20, and on and on... . At other times it will work properly for extended periods. I'm typically only using it for selection. The off/on cycle is so erratic at times that it can't be used. But finger selection always works. I have changed the battery. The small dot on the screen does follow the off/on cycling. Solution ?