If you are using the 600, the top of your pen unscrews (in theory) and it has a reset pin in there. I have weak hands, so I haven't been able to do it.
BUT, my cover has a suede inside and I keep a pin slipped in. I've only used it once - but it involved my computer not recognizing my reader anymore.
Could it be a temperature issue?
I know the manual mentions an operating range of temperatures ... I've kept mine from sitting in a hot car just to be safe.