I'm trying to execute a stored procedure (against SQL Server 2005 through the ODBC driver) and I recieve the following error:

Procedure or Function 'GetNodeID' expects parameter '@ID', which was not supplied.

@ID is the OUTPUT parameter for my procedure, there is an input @machine which is specified and is set to null in the stored procedure:

ALTER PROCEDURE [dbo].[GetNodeID] 
@machine nvarchar(32) = null,
@ID int OUTPUT
AS
BEGIN
SET NOCOUNT ON;

IF EXISTS(SELECT * FROM Nodes WHERE NodeName=@machine)
BEGIN
    SELECT @ID = (SELECT NodeID FROM Nodes WHERE NodeName=@machine)
END
ELSE
BEGIN
    INSERT INTO Nodes (NodeName) VALUES (@machine)
    SELECT @ID = (SELECT NodeID FROM Nodes WHERE NodeName=@machine)
END
END

The following is the code I'm using to set the parameters and call the procedure:

        OdbcCommand Cmd = new OdbcCommand("GetNodeID", _Connection);
        Cmd.CommandType = CommandType.StoredProcedure;

        Cmd.Parameters.Add("@machine", OdbcType.NVarChar);
        Cmd.Parameters["@machine"].Value = Environment.MachineName.ToLower();

        Cmd.Parameters.Add("@ID", OdbcType.Int);
        Cmd.Parameters["@ID"].Direction = ParameterDirection.Output;

        Cmd.ExecuteNonQuery();
        _NodeID = (int)Cmd.Parameters["@Count"].Value;

I've also tried using Cmd.ExecuteScalar with no success. If I break before I execute the command, I can see that @machine has a value.

If I execute the procedure directly from Management Studio, it works correctly.

Any thoughts? Thanks