If you have an Oracle Client (ODAC) installed, you may see an application error when loading the SQL Monitor Web UI.
Open the SQL Monitor web.config in the SQL Monitor website folder,
C:\Program Files\Red Gate\SQL Monitor\Web\Website\ by default, and just before the end add the following:
<healthMonitoring> <providers> <remove name="OracleWebEventProvider"/> </providers> </healthMonitoring> (</system.web> )
then restart both the SQL Monitor Basemonitor and the SQL Monitor Web Service services.