Zebra ZPL print job fails intermittently

Question

I am generating ZPL labels in a C# windows service. The service is simple in srtucture... it uses the System.IO.FileSystemWatcher to detect when a new file is created by our ERP, it then parses the file, gets a chunk of data from SQL about thie job and formats this into validated ZPL.

It then uses the StreamWriter and TcpClient classes to create a connection to a Zebra label printer and sends the ZPL to port 9100. This is a technique we have used in the past without issue.

We use exclusively Zebra GK420D printers.

Here is the weird bit. Sometimes, when the job is sent to the printer, the LED just flashes - no label is printed. If you look at the configuration page in the web interface for that printer, it reports it is busy processing a job. the job appears in the job log absolutely fine, but the printer is seized up. You can't print a config label (as you would usually by holding down the feed button for a few seconds). You can reboot the printer, resubmit the job, and it will print... but this is not guaranteed. Frequently it will just flash again. You can send the same ZPL to another printer and it will print fine.

The ZPL being produced is around 4000 - 4500 bytes long. We have validated the ZPL using online tools to reproduce the label we want to print, and they all appear to be fine.

Has anyone seen anything like this before? It is baffling us here...

Answer 1

Check the firmware on the printer to make sure it's the most current. It sounds like you're doing the right things, even with the pause. I know if you send more data than it has available the printer will stall until it's power cycled.