[SalesForce] Unexpected Identifier for Onclick Javascript button

Merge fields that are strings need to be quoted. Furthermore, it is strongly recommended that you also use JSENCODE if you're not sure that there may be ", ', \, or \n characters.

Specifically:

acct.Related_Lead__c = {!Lead.Name};

Should instead be:

acct.Related_Lead__c = "{!JSNECODE(Lead.Name)}";

(You may choose to use ' or " to surround the string, so long as they match.)

Also, I've noticed you copied some text from a Microsoft Office program; some of your code uses so-called "smart quotes", which look like the following: “ and ”. These won't work in JavaScript, so make sure you replace them with plain " or ' characters.

I could not find a specific issue with your code. I copied and pasted into my org and it works as expected....

{!REQUIRESCRIPT("/soap/ajax/32.0/connection.js")}

     if('{!Account.Active__c}' != 'Yes')
     {
          var c = new sforce.SObject("Account");
          c.id = "{!Account.Id}";
          c.Active__c = true;
          result = sforce.connection.update([c]);
          if ( result[0].getBoolean( "success" ) )
          {
               window.location.reload();
          }
          else
          {
               alert( result[0].errors.message);
          }

     }
     else
     {
          alert("Already True");
     }

I did not make any modification except to change the Object and field name to one in my org. Note Active__c is a picklist in this case not a boolean

I even left the lowercase id and the mixed " and ' as well as the non declared var result

Maybe try with the above using standard fields then verify it works. Once you have it working with standard fields, start adding in your custom fields and see if it breaks.

Another way is to remove all lines of code and add them back in one by one until they break. Once they break, alert the value just before and you should be able to see what is going on.

While not an ideal way to test, the code is short enough that it is completely feasible.