On last print arm of machine, where the registration fork should mount, there will be a stainless steel metal bracket with a yellow square proximity sensor. If it is working, and in the correct position, a red LED light will come on. This lets the printer's PLC know that the wheel is in the up position. Check to make sure this sensor is functioning and adjusted properly.
This sensor can also be checked by going into the hardware test and selecting "Sensor Test", then scroll down until you get to the wheel sensor section:
If the table is up and sensor is working properly, the box under "Wheel Up" will be shaded
If the table is up, but the box is not shaded, the sensor could be bad (adjust or replace sensor)