>> ... a PCL file that Vision sends to the printer. I can send this file to the printer via command line and it behaves exactly the same...1st time I get the bar code, 2nd time I do not.
Sending the contents of your captured invoice.pcl file to your problematic LaserJet M401 exhibits these symptoms.
it would be interesting to know what happens if you send the same file to your other (LaserJet M601) printer, which (according to your earlier thread) works fine with the output from your bespoke Epicor Vision application.