I would make sure that you are using the same version of NPrinting Designer and Server. Those have to be identical so if anything i would suggest you check the version you use to edit template with the version of the NPrinting Server and Engine.
Reinstalling Designer is simple task, but still has to be done following rules which are described in https://help.qlik.com
cheers Lech, When applicable please mark the correct/appropriate replies as "solution" (you can mark up to 3 "solutions". Please LIKE threads if the provided solution is helpful to the problem.