I cannot replicate it at the moment but IIRC this was happening for me when the file was locked. Usually after NP crash - excel/powerpoint process stays in a zombie state and holds the template file locked. Killing the process helps.
1. see Matus hint - this may be one of the issues.
2. what version are you using. NPrtinting June 2017 is out - try the same with it.
HTML and PixelPerfect reports doens't need Office. So, please, try to create an HTML or a PixelPerfect simple report and run a preview.
If you succeed it is an Office installation issue.
If you have the same problem with HTML it means that it is something different than Office.
@Ruggero_Piccoli - when you say "an Office installation issue" what do you mean? We have a customer who's seeing this issue (doesn't work with any Office template editors but fine with HTML) but their Office install seems fine in other respects. Is there a specific thing that needs checking / fixing / installing to resolve this?
If HTML and PixelPerfect report templates are working correctly and only Microsoft Office are not there is an issue with Office installation. Experience suggest to install again Office in the computers where you use Qlik NPrinting Designer and be sure you are installing a supported version.
I don't know what is the specific issue.
Have to say I was sceptical that it would work, but a repair of the Office installation did indeed fix the issue.
God to know that you solved!
I had the same problem using a third screen on windows 10, disbaling the third screen and also setting the default scale and layout to the remaining screens in windows to 100% fixed it for me.
The error message was quite misleading in my case