NVarchar And SelectedValue And InsertCommand

Hi guys,
I've got a  problem  inserting data into my db.
I've created a NVARCHAR column and I'm using SelectedValue Parameters.
I only have a problem in the INSERT mode.
The UPDATE and DELETE are working fine.
All the fields can be updated or deleted, but I can't insert new data inside my db.
I've changed one column to NVARCHAR :   "reference"
I use NVARCHAR because I have some Arabic Fields (unicode) into my db.
But I've copy-pasted everything about the SqlDataSource.
10x a lot anyway !

 ASP.NET using MS Visual Studio 2005 :

.... 
<asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>"

        OldValuesParameterFormatString="original_{0}"
        OnDeleted="SqlDataSource2_Deleted"
        OnUpdated="SqlDataSource2_Updated"
        OnInserted="SqlDataSource2_Inserted"
        SelectCommand=
            "SELECT [reference], [ddf], [description], [quantity], [pru], [supname], [catname]
                FROM [Products]
                WHERE ([reference] = @reference)"
        InsertCommand="INSERT INTO [Products]
                ([reference], [ddf], [description], [quantity], [pru], [supname], [catname])
                VALUES (@reference, @ddf, @description, @quantity, @pru, @supname, @catname)"
        UpdateCommand="UPDATE [Products]
                SET [ddf] = @ddf,
                    [description] = @description,
                    [quantity] = @quantity,
                    [pru] = @pru,
                    [supname] = @supname,
                    [catname] = @catname
               WHERE [reference] = @original_reference"
               DeleteCommand="DELETE FROM [Products] WHERE [reference] = @original_reference">
       
        <SelectParameters>
            <asp:ControlParameter ControlID="GridView1" Name="reference" PropertyName="SelectedValue" Type="String" />     
        </SelectParameters>
       
        <InsertParameters>
            <asp:Parameter Name="reference"
                Type="String" />
            <asp:Parameter Name="ddf"
                Type="DateTime" />
            <asp:Parameter Name="description"
                Type="String" />
            <asp:Parameter Name="quantity"
                Type="String" />
            <asp:Parameter Name="pru"
                Type="Decimal" /> 
            <asp:Parameter Name="supname"
                Type="String" /> 
            <asp:Parameter Name="catname"
                Type="String" />
        </InsertParameters>
       
        <UpdateParameters>
            <asp:Parameter Name="ddf"
                Type="DateTime" />
            <asp:Parameter Name="description"
                Type="String" />
            <asp:Parameter Name="quantity"
                Type="String" />
            <asp:Parameter Name="pru"
                Type="Decimal" /> 
            <asp:Parameter Name="supname"
                Type="String" /> 
            <asp:Parameter Name="catname"
                Type="String" />
            <asp:Parameter Name="original_reference"
                Type="String" />  
        </UpdateParameters>
       
        <DeleteParameters>
            <asp:Parameter Name="original_reference"
                Type="String" />
        </DeleteParameters>
       
    </asp:SqlDataSource>

SQL SERVER 2005 : Create Database File


USE master
GO

IF EXISTS(SELECT * FROM sysdatabases
        WHERE name='Products')
    DROP DATABASE Products
GO

CREATE DATABASE Products
ON (    NAME=Product,
    FILENAME = 'C:WebAppApp_DataProducts.mdf',
    SIZE=10 )
GO

USE Products
GO

CREATE TABLE Categories (
    catname         VARCHAR(25)     NOT NULL,
    PRIMARY KEY (catname) )
GO

CREATE TABLE Suppliers (
    supname        VARCHAR(25)    NOT NULL,
    tel            VARCHAR(50)    ,
    cell        VARCHAR(50)    ,
    fax            VARCHAR(50)    ,
    pob            VARCHAR(25)    ,
    address        VARCHAR(300)    ,
    nearby        VARCHAR(100)    ,
    website        VARCHAR(100)    ,
    email        VARCHAR(100)    ,
    skypephone    VARCHAR(100)    ,
    PRIMARY KEY (supname) )
GO

CREATE TABLE Products (
    reference     NVARCHAR(25)     NOT NULL,
    ddf         DATETIME        NOT NULL,
    description VARCHAR(50)     NOT NULL,
    quantity     VARCHAR(10)     NOT NULL,
    pru         MONEY             NOT NULL,
    supname        VARCHAR(25)    NOT NULL,
    catname        VARCHAR(25)        NOT NULL,
    pv            MONEY            NOT NULL,
    PRIMARY KEY(reference),
    FOREIGN KEY(catname) REFERENCES Categories(catname),
    FOREIGN KEY(supname) REFERENCES Suppliers(supname) )
GO