Update Stored Procedure Not Working When Called From C#

OK, I have been raking my brains with this and no solution yet. I simply want to update a field in a table given the record Id. When I try the SQL in standalone (no sp) it works and the field gets updated. When I do it by executing the stored procedure from a query window in the Express 2005 manager it works well too. When I use the stored procedure from C# then it does not work:

 1. ExecuteNonQuery() always returns -1
 2. When retrieving the @RETURN_VALUE parameter I get -2, meaning that the SP did not find a matching record.

So, with #1 there is definitely something wrong as I would expect ExecuteNonQuery to return something meaningful and with #2 definitely strange as I am able to execute the same SQL code with those parameters from the manager and get the expected results.

Here is my code (some parts left out for brevity):1 int result = 0;
2 if (!String.IsNullOrEmpty(icaoCode))
3 {
4 icaoCode = icaoCode.Trim().ToUpper();
5 try
6 {
7 SqlCommand cmd = new SqlCommand(storedProcedureName);(StoredProcedure.ChangeAirportName);
8 cmd.Parameters.Add("@Icao", SqlDbType.Char, 4).Value = newName;
9 cmd.Parameters.Add("@AirportName", SqlDbType.NVarChar, 50).Value = (String.IsNullOrEmpty(newName) ? null : newName);
10 cmd.Parameters.Add("@RETURN_VALUE", SqlDbType.Int).Direction = ParameterDirection.ReturnValue;
11 cmd.Connection = mConnection; // connection has been opened already, not shown here
12 cmd.CommandType = CommandType.StoredProcedure;
13 int retval = cmd.ExecuteNonQuery(); // returns -1 somehow even when RETURN n is != -1
14 result = (int)cmd.Parameters["@RETURN_VALUE"].Value;
15
16 }
17 catch (Exception ex)
18 {
19 result = -1;
20 }
21 }


 And this is the stored procedure invoked by the code above:1 ALTER PROCEDURE [dbo].[ChangeAirfieldName]
2 -- Add the parameters for the stored procedure here
3 @Id bigint = null,-- Airport Id, OR
4 @Icao char(4) = null,-- ICAO code
5 @AirportName nvarchar(50)
6 AS
7 BEGIN
8 -- SET NOCOUNT ON added to prevent extra result sets from
9 -- interfering with SELECT statements.
10 SET NOCOUNT ON;
11
12 -- Parameter checking
13 IF @Id IS NULL AND @Icao IS NULL
14 BEGIN
15 RETURN -1;-- Did not specify which record to change
16 END
17 -- Get Id if not known given the ICAO code
18 IF @Id IS NULL
19 BEGIN
20 SET @Id = (SELECT [Id] FROM [dbo].[Airports] WHERE [Icao] = @Icao);
21 --PRINT @id
22 IF @Id IS NULL
23 BEGIN
24 RETURN -2;-- No airport found with that ICAO Id
25 END
26 END
27 -- Update record
28 UPDATE [dbo].[Airfields] SET [Name] = @AirportName WHERE [Id] = @Id;
29 RETURN @@ROWCOUNT
30 END


 As I said when I execute standalone UPDATE works fine, but when approaching it via C# it returns -2 (did not find Id).