This generally occurs when the imager is not being detected by the Ann Arbor Digital Devices Software.
The first step is to run though the troubleshooting guide located below:
Imager Connection Error Sheet
If that does not work then inspect the wires for any damage, kinks or cuts that could be preventing communication.
(If the issue is occuring on a model 128s check the power adapter, the black box, for any loose connections or rattling noises)
Should damaged wires be the cause you may send an email to the support department for a repair quote.
This section is for A2D2 Software Error Codes and general troubelshooting. (It will be continually updated)