Check all of your connections, including your switch cable (if you have one) and the USB cable on the back of your docking station. If you have M&M or bliss wheels, check that you have a grounding wire:
The grounding kits have a small metal clip, which is placed on one of
the screws that go through the back axle into the head of the machine,
which grounds the head wheels to the machine head. One end of the
grounding cable attaches to the back axle of the carriage and the other
end attaches to the machine head, grounding the back carriage wheels.
If you do not have one, they can be obtained from APQS.
For continuing problems, please upload your logs on the support page.