Probleme __designer :

Bonjour;

A koi sert __designer:"....."?

J'ai une erreur du type :
Error 2 Unrecognized tag prefix or device filter '__designer'.

MOn code :

Code:

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<asp:Panel id="Panel1" runat="server" __designer:wfdid="w7" Width="125px" Height="50px"><br />
<asp:ImageButton id="CreateMail" onclick="CreateMail_Click" runat="server" Visible="False" ImageUrl="~/images/CreationMail.gif" ImageAlign="Left"></asp:ImageButton>
 <asp:ImageButton id="clearMail" onclick="clearMail_Click" runat="server" Visible="False" ImageUrl="~/images/clearMail.gif" __designer:wfdid="w6" ImageAlign="Left"></asp:ImageButton></asp:Panel>

Pourriez vous m'aider merci????