Sometimes after an install, you might have an issue with NTA views being duplicated. What happens is that some resources are duplicated in the views and prompt the error below:
Unexpected Website Error. Object Reference not set to an Instance of an Object.
NTA 4.x +
This issue occurs due to duplicate resources in the views or duplication views for NTA.
1. Go to Settings > Manage Views.
2. Edit each Netflow view and remove duplicate resources.