I believed this is an IIS related issue:
Orion is looking on this file: C:\inetpub\SolarWinds\Orion\NetPerfMon\Alerts.aspx
Have you tried to rebuild the IIS?
You may want to try the following below:
1. Stop IIS service
2. Go to C:\inetpub\Solarwinds
3. Rename the Solarwinds Folder to Solarwinds_Old
Then run the Configuration Wizard to rebuild the Website. Just select 3 option and let the Configuration Wizard finish.