Output parameter value wrong

I am passing a value to a parameter in a Stored Procedure and also declaring it's direction as ParameterDirection.InputOutput. In the Stored Procedure, the parameter is also declared as an OUTPUT parameter and the value being returned from the Stored Procedure is correct. I know this because I have tested executing the Stored Procedure on its own and using PRINT to display different values throughout the procedure. Also, the final part of the Stored Procedure inserts a record into the database using the value that I am expecting to be returned and that is appearing as expected. However, when I attempt to retrieve the value from the parameter after the SqlCommand has been executed, the value is still the previous value that I passed to the Stored Procedure. I have done this before and I am sure I've done it no differently. Here's a part of my command:

Dim cmd As New SqlCommand("StoredProcedure", Conn)
cmd.CommandType = CommandType.Stor开发者_Go百科edProcedure
cmd.Parameters.Add("@FileName", SqlDbType.NVarChar).Value = ImageFileNameNoExt
cmd.Parameters("@FileName").Direction = ParameterDirection.InputOutput
cmd.ExecuteNonQuery()
ImageFileName = cmd.Parameters("@FileName").Value

Here, I am expecting ImageFileName to be the value of the @FileName parameter, returned from the Stored Procedure. However, it's still the same value as ImageFileNameNoExt which was passed to the procedure in the first place.

Can someone please tell me what I'm doing wrong? Thanks.

EDIT

ALTER PROCEDURE [dbo].[sp_ContentPages_Images_Update]
    @PageID int
    ,@FileName nvarchar(100) OUTPUT
    ,@Ext nvarchar(100)
AS
BEGIN
    SET NOCOUNT ON;

    --As the FileName is a unique key, ensure that the value being entered into the database will be unique.
    --If its not, then we can generate a new one
    SET @FileName = REPLACE(@FileName, ' ', '-')
    DECLARE @i int
            ,@FileNameCheck nvarchar(200)
    SET @i = 2
    SET @FileNameCheck = @FileName + @Ext
    WHILE (SELECT COUNT(*)
        FROM [ContentPages_Images]
        WHERE [FileName]=@FileNameCheck
        AND (@PageID IS NULL OR NOT @PageID=ID)
        ) > 0
    BEGIN
        SET @FileNameCheck = @FileName + '-' + CAST(@i as nvarchar(3)) + @Ext
        SET @i = @i + 1
    END

    SET @FileName = @FileNameCheck

    --Get new layout value
    DECLARE @Layout int
    SET @Layout = 1
    IF (SELECT COUNT(*) FROM [ContentPages_Images] WHERE PageID=@PageID) > 0
    BEGIN
        SET @Layout = (SELECT MAX(Layout) FROM [ContentPages_Images] WHERE PageID=@PageID) + 1
    END

    INSERT INTO [ContentPages_Images]
    (PageID, [FileName], [Layout])
    VALUES
    (@PageID, @FileName, @Layout)

END

---

This is most likely because you haven't specified a size for the parameter. Try changing your code to include the parameter's size like the following:

cmd.Parameters.Add("@FileName", SqlDbType.NVarChar, 100).Value = ImageFileNameNoExt