When I've gotten that error, it is usually because either:
1) I had a program still running that was holding the device open while I was also trying to talk to it in the Phidget control panel
or
2) I had the control panel open and then ran my program, which then couldn't access the device due to the control panel using it.
I'd double-check that there isn't an invisible process that is holding the device open somewhere.
