Hello Paul,
I searched for known issues with the WindSetROI functions, but I was not able to find any.
What versions of LabVIEW and Vision are you using? Can you reproduce the crash with a simple program that reads an image in from file and sets the ROI in a loop? If not, can you strip down the application to the bare minimum that reproduces the crash (remove everything not related to the crash)? If you can get your app small enough, I should be able to run it here and try to reproduce the issue.
Either way, let me know so I can continue to help you out.
Best Regards,
Jesse D.
Applications Engineering
National Instruments