Checkbox Custom Validation is Bypassing Server Validation on Production ASP.NET C# -

my custom validation checkbox not working when put code in production. works on local machine perfectly, cannot determine problem when gets put production server. down below code.

c#

public void checkboxrequireservervalidate(object source, servervalidateeventsargs args) {   args.isvalid = (checkthisbox.checked == true); } 

asp.net

<asp:checkbox id="checkthisbox" text="textholder" runat="server"></asp:checkbox> <asp:customvalidator id="checkboxrequired" runat="server" onservervalidate="checkboxrequireservervalidate" errormessage="you must select box proceed."></asp:customvalidator>