What's error 6522? It's the error that you always get from an unhandled exception in a SQLCLR stored procedure. If I write a SQLCLR error that throws an unhandled exception (let's write one on purpose):

public static void ErrorExecute()
    SqlCommand cmd = SqlContext.GetCommand();
    // everyone knows Bob can't type
    cmd.CommandText = "select * from authorss";

using it from T-SQL:

execute errorexecute
print @@error


Msg 208, Level 16, State 1, Line 0
Invalid object name 'authorss'.
Msg 6522, Level 16, State 1, Procedure ErrorExecute, Line 1
A .NET Framework error occurred during execution of user defined routine or aggregate 'ErrorExecute':
System.Data.SqlServer.SqlException: Invalid object name 'authorss'.
   at System.Data.SqlServer.Internal.StandardEventSink.HandleErrors()
   at System.Data.SqlServer.Internal.RequestExecutor.HandleExecute(EventTranslator eventTranslator, SqlConnection conn, SqlTransaction tran, ClrLevelContext clrlvlctxtPipe, UrtExecutionType uetType, InternalResultSetOptions irsoOpts, CommandBehavior eBehavior, Object& objResult)
   at System.Data.SqlServer.Internal.RequestExecutor.ExecuteToPipe(SqlConnection conn, SqlT.

Not that @@ERROR returns 6522, NOT 208. If you write an equivalent bad T-SQL proc:

create procedure errortsql
– cant type any better in TSQL
select * from authorss

execute errortsql
print @@error

returns 208.

Why does this matter? Say that I have a T-SQL stored procedure (not this one, obviously) that I want to replace with a SQLCLR equivalent that say, runs faster. Say the procedure is used in 20 places in my application, each with semantics that check for specific values of @@ERROR. Won't work the same.

You can't catch the exception in SQLCLR and throw the "correct" one (using a SqlCommand with CommandText of RAISERROR(…)) either, because you can't throw a 208 error (or any other system error) with RAISERROR. So I'll have to change each one of my caller procs too when I switch to SQLCLR. The only current workaround is to change to the new T-SQL try-catch syntax

  EXECUTE errorexecute
  — prints 208, whew…
  PRINT CONVERT(varchar(10), error_number())

Hopefully this will be changed or a workaround in SQLCLR will be available in the next beta. I want @@ERROR to somehow return 208, not 6522. Or this will be a great motivator for everyone to change to T-SQL TRY-CATCH.