<script runat="server">
protected void OnCLick(object sender, EventArgs e)
{
Test.Items[0].Enabled = !Test.Items[0].Enabled;
Response.Write("Button is " + Test.Items[0].Enabled);
}
</script>
<telerik:RadScriptManager ID="MainRSM" runat="server" EnableScriptCombine="true" EnableCdn="false" AsyncPostBackTimeout="500" EnableEmbeddedjQuery="true" OutputCompression="AutoDetect" />
<telerik:RadToolBar Id="Test" runat="server">
<Items>
<telerik:RadToolBarButton>
<ItemTemplate>
<telerik:RadButton runat="server" Text="Test" />
</ItemTemplate>
</telerik:RadToolBarButton>
</Items>
</telerik:RadToolBar>
<telerik:RadButton runat="server" Text="Enable/Disable button" OnClick="OnCLick" />