Τάσο αυτό ακριβώς βρήκα..
<asp:Panel ID="Panel1" runat="server" DefaultButton="Button3">
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:Button ID="Button3" runat="server" Text="psakse kafe" onclick="Button3_Click" />
</asp:Panel>
Είσαι ωραίος. Ευχαριστώ!!!!!!!