Recently I migrated the SolarWinds NPM Database from SQL 2008 to a SQL 2012 instance. Everything went fine until a week later, my client was needing Netflow data to troubleshoot a circuit saturation issue. All of the NTM charts were empty!
It turns out that since the Netflow DB was on a separate server it needed to be re-pointed to the new SolarWinds NPM instance.
To do this required RDP to the NTM DB server and running the NTM Configuration Wizard. It was pretty straightforward, but not obvious in the original SolarWinds DB migration.
Maybe this can save someone else the trouble of this issue and opening a support case.