Hi
You need to provide validation group for (TextBox1,Button1) and (TextBox2,Button2)
<asp:Button ID="Button1" runat="server" ValidationGroup="Grp1" Text="Button" />
<asp:TextBox ID="TextBox1" runat="server" ValidationGroup="grp1"></asp:TextBox>
<asp:Button ID="Button2" runat="server" ValidationGroup="Grp2" Text="Button" />
<asp:TextBox ID="TextBox2" runat="server" ValidationGroup="grp2"></asp:TextBox>
Thanks,
Imdadhusen