I just purchased the G-Pen F610 tablet yesterday and I have this problem...
I could not set an offset for the pen. Right after installation it was working properly, and was following the pen (without touching the tablet). However, after several reboots it stopped. I had to touch the tablet for the cursor to move. In addition, if you press a button on the pen it does moves without touching.
And I tried pretty much everything, I installed the latest driver from the website, I even reinstalled my windows (windows 7 x64 bit), and I also installed windows xp to make sure I didn't forgot anything.
I hope you can help me, because the tablet is now useless to me