SQL Scope_Identity is returning 0 or -1

Question

I'm having issues getting the last row affected ID, it's returning 0, this means that it has an error on format being inserted. I executed the stored procedure and added the values manually, it return'd the correct ID. But when I try to do it with the code it keeps returning 0 or -1 ... I tried this last night after several hours and I'm already confused with the values it gave me.

C#:

conn.Open();

            cmd.Parameters.AddWithValue("@fileName", fileName);
            cmd.Parameters.AddWithValue("@filePrivacy", filePrivacy);

            cmd.Parameters.AddWithValue("@filePassword", filePassword);

            cmd.Parameters.AddWithValue("@fileDescription", fileDesc);
            cmd.Parameters.AddWithValue("@fileOwner", fileOwner);
            cmd.Parameters.AddWithValue("@fileDate", DateTime.Now);
            cmd.Parameters.AddWithValue("@fileExpire", DateTime.Now.AddMinutes(fileExpire));
            cmd.Parameters.AddWithValue("@fileCodeText", fileType);
            var fileID = cmd.Parameters.Add("@fileID", SqlDbType.Int);
            fileID.Direction = ParameterDirection.Output;

            int returnfileID = (int)cmd.ExecuteScalar();
            return returnfileID;

Stored Procedure:

CREATE PROCEDURE [dbo].[Upload]
@fileName nvarchar(20),
@filePrivacy int,
@filePassword nvarchar(50),
@fileDescription nvarchar(200),
@fileOwner nvarchar(14),
@fileDate smalldatetime,
@fileExpire smalldatetime,
@fileCodeText int,
@fileID int out

AS
INSERT INTO Files ([FileName], FilePrivacy, FilePassword, FileDescription, FileOwner, FileDate, FileExpire, FileCodeText)
VALUES (@fileName, @filePrivacy, @filePassword, @fileDescription, @fileOwner, @fileDate, @fileExpire, @fileCodeText)
SET @fileID = SCOPE_IDENTITY()
RETURN @fileID

SQL Table:

CREATE TABLE [dbo].[Files] (
[Id]              INT            IDENTITY (1, 1) NOT NULL,
[FileName]        NVARCHAR (20)  NOT NULL,
[FilePrivacy]     INT            NOT NULL,
[FilePassword]    NVARCHAR (50)  NULL,
[FileDescription] NVARCHAR (200) NULL,
[FileOwner]       NVARCHAR (14)  NOT NULL,
[FileDate]        SMALLDATETIME  NOT NULL,
[FileExpire]      SMALLDATETIME  NOT NULL,
[FileCodeText]    INT            NOT NULL,
PRIMARY KEY CLUSTERED ([Id] ASC)
);

Answer 1

ExecuteScalar 'Executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored'

If you select @fileID (instead of return) it should work.
Alternatively you could access the @fileID parameter value after you execute the query, in which case there's no real point having an ExecuteScalar, you could change it to to ExecutenonQuery.