What does error code 103 mean on a datacard printer sd360 mean? How do I troubleshoot?

Usually that occurs when the card position sensors inside the printer need a thorough cleaning. Get yourself a Datacard cleaning kit for the SD260/SD360 printers, and perform a standard cleaning with it - PLUS - use IPA alcohol soaked wipes to clean the "slot" in the card sensors where the card passes through during printing. That should take care of things.

If cleaning DOESN'T resolve the issue, and you either have extremely high print volumes on the machine (>100,000 cards), OR if it is more than 3 or 4 years old, then it could be the internal transport rollers are worn to the point that they are not consistently positioning the card properly. If that's the case, warranty will cover it (if still in effect), or otherwise repair or replace.