Seeing as you are using a conditional update panel, you can try either of these after putting the buttons inside an update panel.
protected void ApplyAssociation(object sender, EventArgs e)
{
//Some piece of code
if (a == 0)
{
ButtonAssociateRules.Style["visibility"] = "hidden";
ButtonReplaceId.Style["visibility"] = "hidden";
myUpdatePanel.Update();
}
}
protected void ApplyAssociation(object sender, EventArgs e)
{
//Some piece of code
if (a == 0)
{
ButtonAssociateRules.Visible = false;
ButtonReplaceId.Visible = false;
myUpdatePanel.Update();
}
}
Here's an example of your buttons inside an update panel.
<asp:UpdatePanel ID="myUpdatePanel" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<div style="padding-left:400px;">
<asp:Button ID="ButtonAssociateRules" runat="server" OnClick="AssociateMultipleRulesButtonClick"
CssClass="search_button_in_vm_intersection" Text="Associate Multiple Rules"
OnClientClick="return OnClientClickAssociateRewardRuleFile();" />
<asp:Button ID="ButtonReplaceId" runat="server" OnClick="ApplyReplaceIfRuleIntersects"
CssClass="search_button_in_vm_intersection" Text="Replace Previous Rules"
OnClientClick="return OnClientClickReplaceRewardRuleFile();" />
</div>
</ContentTemplate>
</asp:UpdatePanel>