Two possible reasons that I can remember:
1. You are using an unsupported QlikView version like 11.0.x. Or
2. If you are using NPrinting version 16.0 IR or SR1 this is a known issue that was fixed in SR2. From the SR2 Release Notes: A “Syntax Error” appeared when an On-Demand report was requested and no selections were applied in the QVW. This issue has been resolved, but to correct this problem, you must re-create your On-Demand objects after installing the new version of the components.
HTH - Daniel.