Duplicate serialized labels printing in a high volume production environment on Zebra printers can have significant issues in some environments resulting in charge backs and returned shipments.
The duplicates seem to happen randomly and there are no errors in Loftware. Capturing the Zebra print stream will show that the correct data was all sent by Loftware Print Server and received by the printer. The duplicate printing is only happening when the printer runs out of label or ribbon stock midway though a run of labels. When the printer detects the outage it will mark the label it was printing as "incomplete" and when the printer is restarted the "incomplete" job is reprinted, even if the "incomplete" job did finish printing. This condition is most common with labels that are short (i.e. 1 inch high).
There is a command string that can be sent to the printer that will disable the "Reprint After Error" setting which is on by default.
Create a text file with the following lines:
ZPL Command String
^XA ^DFE:AUTOEXEC.ZPL^FS ^JZN^XZ
Copy or FTP the file to the printer to permanently disable the "Reprint After Error" setting.
After this setting is changed the "incomplete" label will not be printed when printing resumes.