Output Parameter?

A SQL Server 2005 DB table named "Users" has the following columns:


ID - int (IDENTITY)
FirstName - varchar(50)
LastName - varchar(50)
UserID - varchar(20)
Password - varchar(20)


Before inserting a new record in the DB table, ASP.NET first checks whether the UserID supplied by the new record already exists or not. If it exists, the new record shouldn't be inserted in the DB table & the user should be shown a message saying UserID already exists. To do this, ASP.NET uses a stored procedure. If the value returned by the stored procedure is 1, it means that the UserID already exists. If the value returned by the stored procedure is 0, then the new record should be inserted in the DB table. This is how I have framed the stored procedure:


CREATE PROCEDURE RegUsers
        @FName varchar(50),
        @LName varchar(50),
        @UserID varchar(50),
        @Password varchar(50),
        @return_value int OUTPUT
AS
        IF EXISTS(SELECT UserID FROM Users WHERE UserID=@UserID)
        BEGIN
                SET @return_value=1
        END
        ELSE
        BEGIN
                SET @return_value=0
                INSERT INTO Users VALUES (@FName,@LName,@UserID,@Password)
        END


& this is how I am invoking the stored procedure from the ASPX page:


<script runat="server">
    Sub btnSubmit(ByVal obj As Object, ByVal ea As EventArgs)
        Dim sqlCmd As SqlCommand
        Dim sqlConn As SqlConnection


        sqlConn = New SqlConnection("Data Source=MyDBSQLEXPRESS;Initial Catalog=DB;Integrated Security=True")
        sqlCmd = New SqlCommand("RegUsers", sqlConn)
        sqlCmd.CommandType = CommandType.StoredProcedure


        With sqlCmd
            Parameters.Add("@return_value", SqlDbType.Int, 4).Direction = ParameterDirection.ReturnValue
            Parameters.AddWithValue("@FName", txtFName.Text)
            Parameters.AddWithValue("@LName", txtLName.Text)
            Parameters.AddWithValue("@UserID", txtUserID.Text)
            Parameters.AddWithValue("@Password", txtPassword.Text)
        End With


        sqlConn.Open()
        sqlCmd.ExecuteNonQuery()


        If (sqlCmd.Parameters(0).Value = 1) Then
            lblMessage.Text = "UserID Already Exists!"
        ElseIf (sqlCmd.Parameters(0).Value = 0) Then
            lblMessage.Text = "Thanks For Registering!"
        End If


        sqlConn.Close()
    End Sub
</script>
<form runat="server">
<%-- the 4 TextBoxes come here -->
</form>


When I execute the above ASPX code, if the UserID I entered already exists in the DB table, then ASPX generates the following error:


Procedure or Function 'RegisterUsers' expects parameter '@return_value', which was not supplied.


pointing to the line


sqlCmd.ExecuteNonQuery()


Can someone please point out where am I going wrong?