Is NPrinting set up to be a trusted app in the MAPI client? This is a requirement if using MAPI.
If you've already done this and still getting the error, please submit this issue to the Qlik Support Desk: Technical Product Support | Qlik
Just to add to what Stephen said, NPrinting supports simple MAPI but requires that a MAPI client (like Outlook) be installed on the local machine, and that the MAPI client "views" NPrinting as a trusted app. In Outlook 2013, you can set trusted apps in:
File>Options>Trust Center> Trust Center Settings>Programmatic access
NB that depending on the security settings in your company you may not have access to the Programmatic Access settings on your computer.
You may also want to check this article from Microsoft support: