In a nutshell this is due to an incompatibility between .NET and Windows. The most likely candidate for the cause would be an upgrade to either Windows or .NET. Overall, check the Windows and SQL Server patch levels. The CLR/.NET that is affected is Microsoft.SqlServer.Types. To poke around to see what else might be at risk, issue these queries from master:SELECT * FROM sys.dm_clr_appdomains;SELECT * FROM sys.dm_clr_loaded_assemblie... * FROM sys.assemblies WHERE principal_id <> 4 AND ......