Closed loop - encoder/position not updating while moving

Hello,
i am currently stuck implementing a direct closed loop (2 axis lathe, parallel port, stepper motor, linear scale for closed loop).
The problem is: I do get the right position feedback, when moving manually (DRO display is correct) and i can see the correct encoder positions (in Hal-Scope: encoder.0.position). However, as soon as i try to move the axis, it starts to move and errors out with following error. If i look in the hal-scope, the "encoder.0.position" does not move one bit during the move (stepper is moving). 

--> Why does read out the position while idling but not while moving ?
Thanks 

maybe the move is to fast or the resolution of the encoder too high for parport