roborun utility and encoders

I have us digital encoders set up. they work. i can see the numbers in the encoder tab. but i can't use the sliders at the bottom to move the motors. i have limit switches hooked up and set them up so that they aren't activated by the device. i can run the motors in the run tab and can flip back to the encoder tab to see the numbers have changed. if i select closed loop i can't run the motors in the run tab or the encoder tab.
any ideas?
thanks,
dominik