The printer is busy. This may be a normal startup cycle or a head cleaning. If the carriage has moved, then the INK button has been pressed. Press the INK button again.
The Epson mainboard believes that the waste tank is full (NOTE: this is not the waste ink bottle on the side of the HM1-C. Rather, this is referring to the waste container from the Epson 2400, which is not present in the DTG). The Epson mainboard counts the volume of ink going through the capping station, and will not print until the waste tank is reset. ( link to Waste Tank reset page here).
The gap sensor has detected a wrinkle, fiber or something else obstructing it. Remove the obstruction. Press the UP button to have the HM1-c automatically set its correct printing height. The printer will now resume printing.
The printer has experienced a Fatal Error. This may be caused by a number of things. First, attempt to determine what the printer was trying to do at the time of the error:
If the head carriage was in motion, make sure that nothing obstructed the head carriage's movement. Thoroughly clean the encoder strip, and replace it if it is at all scratched, or otherwise damaged.
If the upper unit was moving (front to back), make sure that nothing has blocked its motion. Examine the drive belts on each side and make sure that nothing has lodged in the teeth of the belt. Contact Technical Support for instructions on cleaning the PF Encoder.
Power the printer completely off for 30 seconds (both upper and lower units), and then power back on. If the error has not cleared, contact Technical Support.