Removing same item from two dropdown list

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ASP.NET

Hi to all, i am adding two dropdown list in my registration form. the first dropdownlist is bind to database, and second dropdownlist also from same table. if i select a item from firstdropdownlist it remove the item from second dropdownlist. That is Ok for me, but the problem is that i click all item of firstdropdown list than the second dropdownlist become empty.. See my code

<asp:DropDownList ID="DrpPrefLangauge1"
                  AppendDataBoundItems ="true"
                  OnSelectedIndexChanged="DrpPrefLangauge1_SelectedIndexChanged"  
                  runat="server"
                  AutoPostBack="True">
    <asp:ListItem Text="----Select----" 
                  Value="0">
    </asp:ListItem>
</asp:DropDownList> 

<asp:DropDownList ID="DrpPrefLangauge2"
                  AppendDataBoundItems="true"
                  runat="server">
    <asp:ListItem Text="----Select----"
                  Value="0">
    </asp:ListItem>
</asp:DropDownList>

At code behind:

protected void setLangauge()
{
    nsBusinessLogicLayer.LanguageInfo objLanguageInfo = new nsBusinessLogicLayer.LanguageInfo();
    nsAbstractLayer.LanguageInfoAbstract objLanguageInfoAbstract = new nsAbstractLayer.LanguageInfoAbstract();
    //objLanguageInfoAbstract.Languageid = Convert.ToInt64(DrpPrefLangauge1.SelectedValue);

    DataTable dt = objLanguageInfo.Search(objLanguageInfoAbstract);

    DrpPrefLangauge1.DataSource     = dt;
    DrpPrefLangauge1.DataTextField  = "LanguageName";
    DrpPrefLangauge1.DataValueField = "Languageid";
    DrpPrefLangauge1.DataBind();

    DrpPrefLangauge2.DataSource     = dt;
    DrpPrefLangauge2.DataTextField  = "LanguageName";
    DrpPrefLangauge2.DataValueField = "Languageid";
    DrpPrefLangauge2.DataBind();
}

ON selected index:

protected void DrpPrefLangauge1_SelectedIndexChanged(object sender, EventArgs e)
{
    ListItem  value = DrpPrefLangauge1.SelectedItem;
    //int index=DrpPrefLangauge2.Items.IndexOf(value);
    DrpPrefLangauge2.Items.Remove(value);
}

I want if i select say hindi langauge from firstdownlist , it will remove in second dropdownlist.. this is working but if i select all item from my first downlist the second dropdownlist become empty..that is the problem how it solve it..