Hello, please see Article 000045598 in Qlik's Support Portal.
The error " System.OutOfMemoryException " seems to happen because the process is unable to find a large enough section of *contiguous* unused pages in its virtual address space to do the requested mapping (not because of the total amount of memory, but rather contiguous unused space), or because a directory or template path is no longer valid. This may cause a memory leak. If the logs do not show an error related to "output producer", than it's usually because of the former.
The error "Error: QlikView NPrinting can't find a supported reporting output producer for the file" in the NPrinting logs demonstrates that there is a directory or template path that is no longer valid, or there is a duplicate template, as these will cause memory leaks... and the customer should update the path.
If you encounter an issue where the NPrinting execution remains in a running status forever, this was a bug (OP-5692) in NPrinting, and the resolution is to upgrade to the November 2017 release or newer. In summary, the report preview execution remained in "running" status forever due to an un-handled and not logged OutOfMemoryException error in Qlik NPrinting Scheduler, which is fixed, and an NPrinting (and QlikView/Qliksense) update to the latest version should be performed.
If the QlikView services are crashing when NPrinting tasks are executed, then it's likely that your QlikView documents are extremely large, charts are maximized, etc... so QlikView Server uses a lot of machine resources and it goes down right when the request from NPrinting is sent. You should try to schedule NPrinting when the Server has more resources. NPrinting uses the QlikView Desktop APIs. If the QlikView Server can't get back to QlikView Desktop, NPrinting shows the error.