Msg 243, Level 16, State 1, Line 1
Type %1! is not a defined system type.
This error message appears when you try to use a datatype that is not known and supported by SQL Server.
The T-SQL statement can be parsed, but causes the error at runtime.
Error of the Severity level 16 are generated by the user and can be fixed by the SQL Server user. The datatype must be known to SQL Server. Either as a system-supplied datatype or as user-defined datatype (UDT; SQL Server 2005).
All versions of SQL Server.
SELECT CAST(‘257’ AS MyType)
In the above example we try to convert the string 257 to the MyType datatype. Because this datatype is neither system-supplied nor known to SQL Server as UDT, the error is raised.