If you face “Problem with Onclick JavaScript ‘No operation available for request…'” issue, check the below

If you have Namespace prefix, you have to write the code as below in the button.

Sample Code:

{!REQUIRESCRIPT(“/soap/ajax/15.0/connection.js”)};
{!REQUIRESCRIPT(“/soap/ajax/15.0/apex.js”)};
alert(sforce.apex.execute(“InfallibleTech.SubscribeOrUnsubscribeLead”,”subscribeLead”,{leadId:”{!Lead.Id}”}));
location.reload(true);

Cheers!!!