I am facing the error saying "A problem with the OnClick JavaScript for this button or link was encountered''

CLASS:
global class customClone
{
    webservice static void cloneAccount(Id acctId) // you can pass parameters
    { 
       List<Contact> cont = new List<Contact>();
       Account acc = [SELECT ID, Name FROM Account WHERE Id = : acctId];
       Account accCopy = acc.clone(false,true);
       accCopy.Name = acc.Name +'-'+system.today();
       insert accCopy;
       
       //cloning Related contact Records
       
       for(Contact c : [SELECT Id, LastName, AccountId FROM Contact WHERE AccountId = : acc.Id]){
         Contact conCopy = c.clone(false,true);
         conCopy.AccountId = accCopy.Id;
         cont.add(conCopy);
        }
       insert cont; 
    }
}

MY JAVASCRIPT CODE for the custom button

{!REQUIRESCRIPT("/soap/ajax/30.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/30.0/apex.js")}
sforce.apex.execute("customClone","cloneAccount",{acctId:{!Account.Id}}"});