When attempting to delete a site in Admin > Site Security we receive the following error message:
The DELETE statement conflicted with the REFERENCE constraint "FK_USR_CLASS_VARIANCECODEID". The conflict occurred in database "Dbo.Name" , table "dbo.USR_CLASS" , column 'VARIANCECODEID'
This error occurs when a built-in process tries to delete something that is referenced by a custom table such as USR_CLASS. Try manually removing the reference to the custom table (VARIANCECODEID), and then re-trying the delete.