NPrinting On-Demand crashes when I add and Extension Objects to the dashboard.

The application crashes adding an extension object (Run button or Queue) in the dashboard.

NPrinting needs some Internet Explorer API to work with Extension Objects. They are available only in the latest Internet Explorer versions.
A correct installation of the On-Demand extension objects is necessary too.
 

An installation of Internet Explorer 10 or 11 on the machine is necessary even if you are using a different browser. Verify that the Internet Explorer version you are using is supported and upgrade it if necessary.

Verify that the Extension Objects are correctly installed if the problem persist. Extension objects are 3 subfolders named NPQueue, NPReport and NPTask in

C:\ProgramData\QlikTech\QlikViewServer\Extensions\Objects\NPrinting

Verify that they are there. The folder must be saved in the machine where NPrinting Server is installed and in the machine where QlikView Server is installed.
Please, reinstall NPrinting Server if you cannot find the extension folders. You can install only the Extension Objects running the QlikView NPrinting Server setup and choosing the "Custom Installation" option.