I've created a button with this java script:
{!REQUIRESCRIPT("/soap/ajax/30.0/connection.js")} 
{!REQUIRESCRIPT("/soap/ajax/30.0/apex.js")} 
sforce.apex.execute("buttonHandler","copyOLItoPP",{id:"{!Opportunity.Id}"}); 
location.reload();

but I keep getting this error whenever I try to click it:
{faultcode:'soapenv:Client; faultstring:'No such parameter id defined for operation. please check the WSDL for the service.'}