#Java Development2 discussing

public static List<State__c> getState(){
        List <State__c> first = [SELECT Id,Name,Child__r.Name FROM State__c];
        List<State__c> uniqueValue = new List<State__c>();
        Set<State__c> myset = new Set<State__c>();
        for (State__cs : first) {
            if (myset.add(s)) {
                uniqueValue.add(s);
            }
        }
        return uniqueValue; 
    }

suucces[{"Id":"a0b5E000002VSuXQAW","Name":"Abbes","Child__c":"a0Z5E000002s12BUAQ","Child__c":{"Name":"Abbes","Id":"a0Z5E000002s12BUAQ"},"Public__c":true},{"Id":"a0b5E000002VSajQAG","Name":"Abbes","Child__c":"a0Z5E000002s12BUAQ","Child__r":{"Name":"Abbes","Id":"a0Z5E000002s12BUAQ"},"Public__c":true}]

We are trying to use the E2Excel "Export to Excel" button (downloaded from the App Exchange) on custom objects and it seems to work if you include it directly on the object, but when we try to lauch the button from a 'Related List' we are getting an error message: 

I have very little experience with Java but here is the code they included in the instructions for installation of the botton on the object:

window.open('apex/E2Ex__Export_To_Excel?idString='+idString+'&sobjid='+sobjid+'&listid='+listId+'&listName='+listName);