Qual erro é este <asp:Button?

Boa tarde.

Sou iniciante em asp.net, alguns erros n ainda não estou me familiarizando.

Este erro acontece quando coloco o comando: OnClick

Server Error in '/' Application.
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Compilation Error
Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.

Compiler Error Message: CS1061: 'ASP.atendimento_aspx' does not contain a definition for 'Inserir' and no extension method 'Inserir' accepting a first argument of type 'ASP.atendimento_aspx' could be found (are you missing a using directive or an assembly reference?)

Source Error:

Line 72: <td></td>
Line 73: <td style="float:right;background:#f2f2f2;">

Line 74: <asp:Button ID="Button2" OnClick="Inserir" runat="server" Text="Button"></asp:Button>

Line 75: </td>
Line 76: </tr>

Source File: c:\Documents and Settings\Administrador\Meus documentos\Visual Studio 2010\Projects\grfb\grfb\atendimento.aspx Line: 74