P4T Thermal Transfer Ignored

We have a couple P4Ts that have begun acting up.  We use ribbon and what has been happening recently is that when a print job is sent the label feeds but there is nothing printed on the label.  I have been playing with one of the printers and noticed that after issuing ~JC^XA^JUS^XZ and restarting the printer it will start printing again for a couple labels and then quit, feeding a blank label... as if it was trying to print direct.


  "firmwareVersion" : "SHCPT11z48          ",

  "firmwareDate" : "02/26/13"


Do you guys have any ideas what could be wrong?