SQL Monitor displays this error when you try to connect from a web server that the base monitor doesn't recognize.

To fix the problem, pair the base monitor with the new web server.

If you want to switch over from an old web server to a new one:

1. On the machine running the base monitor, go to %ProgramData%\Red Gate\SQL Monitor\
2. Delete RedGate.SqlMonitor.AuthorizedClients.config
3. On the web server you want to use, open the SQL Monitor web interface and connect to the base monitor.
   This pairs your current web server to the base monitor.

If you want to connect the Base Monitor with new web server, but keep the connection to the old one:

1. On the machine running the base monitor, go to %ProgramData%\Red Gate\SQL Monitor\
2. Get a thumbprint by doing one of the following steps:
   1. If you are using SQL Monitor version 7.1.17 or above, you can get a thumbprint from the error message "The web server isn't authorized to access this base monitor as the following thumbprint is missing:"
   2. Alternatively, you can get a thumbprint by running the following Powershell command on the machine running the base monitor from %ProgramData%\Red Gate\SQL Monitor\:
      Get-PfxCertificate -FilePath "Red Gate Monitor.pfx"
3. Add a new line with a thumbprint to RedGate.SqlMonitor.AuthorizedClients.config
4. Try to connect again.