I have one requirement  where I want to update cookie from a webmethod. The webmethod is called from ajax using PageMethods.

Here is how my .aspx page looks like

In code behind

 I dont believe this is possible serverside, however, why not set the cookie in the OnSucess javascript method, with the key/value provided from the web-method?

Yes!  It is possible from server side if I remove line 'throw ex' code in the below code. but I was trying to update the cookie on error in webmethod. Something likes this.

try
{ 

}
catch(Exception ex)
{
   HttpContext.Current.Response.Cookies[“ck”].value=”value”;
   throw ex;
}