I tried your suggestion, its not working. Even I closed all browsers, cleared my cache, restarted all QlikNprinting services and restarted my laptop. but still same issue happening.
Adding an extra info about my environment:
I have recently upgraded my Qlik NPrinting from Feb 2021 to May 2021. I facing this error while I edit the report and also I noticed while my designer attempt to open while editing report its opening on Feb 2021 from there the error message popping out.
If you look in the task manager @Purushothaman you will notice that there is an nprinting designer executible in memory. To remove it I suggest to completely restart your computer. The NP designer should open normally after doing so.
Also note that if you upgraded your designer only, this is not supported.
This is because youcanhaveonly a single instance of Qlik NPrinting Designeropen at a time on a computer and you are trying to open a second. - if you have not aDesigneropened check the Windows processes and kill the one related with theDesigner.