Calling Managed CLR Stored Procedure from C++ SQL Server 2008 fails with Msg 2809

Question

I am trying to call a stored procedure from C++ (VS 2010).
Here is what the stored procedure looks like:
public class Validate
[Microsoft.SqlServer.Server.SqlProcedure(Name = "ClientTest")]
public static void ClientTest(out String res )
{ res = "50";}
To create a stored procedure I deploy at first the assembly
USE [test]
GO
CREATE ASSEMBLY ClientTestAssembly
AUTHORIZATION testLogin
FROM 'C:\Users\test\Documents\Visual Studio 2010\Projects\TestCreationAssemblyCSharp\TestCreationAssemblyCSharp\bin\x64\Debug\TestCreationAssemblyCSharp.dll'
and call 
USE test
GO
CREATE PROCEDURE ClientTest (@res NVARCHAR(40) OUTPUT)
AS
EXTERNAL NAME ClientTestAssembly.Validate.ClientTest
I can call my procedure direct in SQL Server Management Studio without any errors
declare @res nvarchar(10)
execute ClientTest @res OUTPUT
print @res
But when I try to call this procedure from C++ using CALL syntax
SQLBindParameter(sqlstatementhandle, 1, SQL_PARAM_OUTPUT, SQL_C_CHAR,
SQL_VARCHAR , 40, 0, version, sizeof(version) ,
&pcbValue);
res = SQLExecDirect(sqlstatementhandle, (SQLCHAR*)("{CALL ClientTest(?) }"), SQL_NTS);
I get the Error 2809 with SQLSTATE 42000 and with statement 
The request for 'ClientTest'
(procedure) failed because 'ClientTest' is a procedure object.
However, if I wrap my CLR stored procedure into a T-SQL stored procedure, like
CREATE PROCEDURE myProc (@res NVARCHAR(40) OUTPUT)
AS
EXEC ClientTest @res OUTPUT
and call then myProc instead of ClientTest
res = SQLExecDirect(sqlstatementhandle, (SQLCHAR*)("{CALL myProc(?) }"), SQL_NTS);
everithing works fine and I get 50 as result.
I have no ideas what is the reason for that behavior.
Thanks very much for any suggestion. 
Christina

Answer 1

I'm not an ODBC expert, but you might try following the sample here:
Process Return Codes and Output Parameters (ODBC)
To see if it also behaves differently for your CLR proc.
David
David http://blogs.msdn.com/b/dbrowne/