I had the same problem for a while. NI's technical support sent me these instructions (copied straight from the email and they fixed the problem):
1. delete NI-Report from my registry
2. delete the folder named ni-reports from ..\National Instruments\shared
3. reinstall the LV 6 Run-Time Engine from the ftp site: http://www.ni.com
-> downloads -> drivers and updates -> LabVIEW
It's a bit of a pain, but I hope it solves your problem.
Rob