Use
ValidationGoup
property.
Eg.:-
<asp:textbox id="txt" runat="server"></asp:textbox>
<asp:requiredfieldvalidator id="rfv" runat="server" errormessage="Enter Name."
Display="Dynamic" SetFocusOnError="true"
ForeColor="Red"
ValidationGroup="Group"
ControlToValidate="txt">
</asp:requiredfieldvalidator>
Use same
ValidationGoup
for your button on which you want to perform validation.
<asp:button id="btnNext" runat="server" text="Next"
ValidationGroup="Group" />
</asp:button>
Or you can set
CausesValidation
property of your link button to false.
Good luck.