I have a similiar problem also. For example, I use Stepper mode with open loop configure in MAX to run a FUJI servo with no problem at all, but once it is configured to close loop in MAX the encoder value doesn't change when monitored from 1D interactive window of MAX. And eventually the following error came out and motor stop!
I have set the correct encoder feedback parameter in Servo drive, and I can read the encoder value by Read Encoder.vi but How come it doesn't show the value in MAX? Is any configuration that I was missed out in MAX? Is need to set the encoder setting in MAX to match the servo encoder output?