You may also see this error message displayed in the views on a page (the page itself loads ok):
Error: Unable to validate data source credentials. Please make sure to provide the right credentials for your data source.This second error is because the views in NV are trying to connect to the pollers web service, and are failing due to the same permission issue that causes the error 500.19 issue on the master.
This is caused by incorrect version of .NET and can be resolved by:
Release: RAIB1H99000-9.1-Network Flow Analysis-Interface Bundle-Hardware