this error occurs at seemingly random times during normal operations when calling _thePrinterSDK.Open(_prnName, out string errMsg) which in turn call's ZBRGetHandle(...). There's no apparent reason for that and it even sometimes happens to me when opening up the application for the first time. Is it safe to WAIT until the Handle is valid? What's the usual way of resolving this error? Is it a sign that the printer hasn't quite finished it's operation yet? Is there any RELIABLE way to tell if the printer is done with the current job and if so why isn't that the way the examples are programmed?