This error typically indicates that the encoder strip is not being detected by the sensor on the back of the printer carriage.  The encoder strip is the clear strip that spans the left to right distance where the printer carriage (cartridge holder) and arm intersect.  The strip has tiny black lines that are read by a sensor on the back of the carriage.  This tells the unit where along the horizontal (left to right) path the arm/and or cartridges are located.  If you receive this error when you start up the unit it probably means that the sensor can not read the encoder strip.  Check the following:

1. Missing Encoder. Make sure the strip is not missing. It may have broken or the spring (far left side) that provides tension may have fallen off.

2. Out of Place Encoder. Ensure it is not twisted as it goes behind the carriage. It could be displaced from the notch behind the carriage. You may be able to put the encoder strip back in place.  It slips in a hidden notch on the back of the carriage from the bottom.  Unfortunately, you are not able to see the notch so you need to put it back in place blindly.  Here is a video on the repair process: https://customercare.primera.com/portal/en/kb/articles/how-to-fix-an-encoder-strip-that-is-out-of-place-on-your-primera-printer

3. Clean the Encoder. Inspect the encoder strip for ink, dirt, or grease that may be blocking the sensor from reading it.  If necessary lightly clean the strip with a mild cleaner.  Do not scrub, since you may clean of the lines that are printed on the strip. 

4. Arm off Frame.  If you push too hard during cartridge installation, the arm may come off the frame if the cartridge carrier is in the middle.  Instead, press the cartridge button on the top of the duplicator to move the cartridge carrier into cartridge change position.  To fix a carrier off the frame, follow the instructions below.