Stored Procedures + Informix

Hello!

I'm trying to execute a stored procedure (on Informix 9.3/4) that returns a value from a c# class. So far, I'm able to execute procedure that doesn't return values, but somehow we can't get a call to a procedure that returns a value to work. I hope some of you can help me.

Here's my stored procedure, it's for adding in a new user in my user table, with creating a record in the history table. The procedure returns the id of the newly created user (the procedure works when run directly on informix)

Code:

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CREATE FUNCTION addUser ( puserid VARCHAR(15), pname VARCHAR(30), ppasswort VARCHAR(50), pemail VARCHAR(50), pid INTEGER)
        RETURNING INTEGER;
        DEFINE iid INTEGER;
        DEFINE datum CHAR(14);

        INSERT INTO adm_benutzer (userid, name, passwort, email) VALUES (puserid, pname, ppasswort, pemail);

        SELECT id INTO iid FROM adm_benutzer where id = (SELECT max(id) FROM adm_benutzer);

        INSERT INTO adm_historie (fkbenutzerid, typ, vorgang, datum) VALUES (pid, 0, "Neuen Benutzer angelegt: ", TODAY);

        RETURN iid;
END FUNCTION;

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Now about my c# class or better the function of my DB access class:

Code:

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public int addUser(string userid, string nachname, string passwort, string email, int execUserid)

{
        OleDbConnection myCon = new OleDbConnection(ConfigurationSettings.AppSettings["ConnectionString"]);
        OleDbCommand myCommand= new OleDbCommand("addUser", myCon);

        // Mark the Command as a SPROC
        myCommand.CommandType = CommandType.StoredProcedure;

        // Add Parameters to SPROC

        // BenutzerId
        OleDbParameter paruserid = new OleDbParameter("",OleDbType.VarChar,15);
        paruserid.Value = userid;
        myCommand.Parameters.Add(paruserid);

        // Name
        OleDbParameter parname = new OleDbParameter("",OleDbType.VarChar,30);
        parname.Value = nachname;
        myCommand.Parameters.Add(parname);

        // Passwort
        OleDbParameter parpw = new OleDbParameter("",OleDbType.VarChar,50);
        parpw.Value = passwort;
        myCommand.Parameters.Add(parpw);

        // Email
        OleDbParameter paremail = new OleDbParameter("",OleDbType.VarChar,50);
        paremail.Value = email;
        myCommand.Parameters.Add(paremail);


        // Return Value - neue Id des Benutzers
        OleDbParameter parId = new OleDbParameter("iid",OleDbType.Integer,4);
        parId.Direction = ParameterDirection.ReturnValue;
        myCommand.Parameters.Add(parId);


        try
        {
                // Open the connection and execute the Command
                myCon.Open();
                myCommand.ExecuteNonQuery();
        }
        catch(Exception ex)
        {
                string a = ex.Message;
                // failed to create a new user
                return -1;
        }
        finally
        {               
                // Close the Connection
                if (myCon.State == ConnectionState.Open)
                myCon.Close();
        }

        return (int) parId.Value;
}

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Any help would be greatly appreciated!!! Thanks a lot!
Nina