WebHelp 5.10.001 JavaScript runtime error

Using WebHelp 5.10.001 (Adobe RoboHelp 11, WebHelp 5.50) and am receiving the following error:

JavaScript runtime error: Object doesn't support property or method 'RegisterListener'

The above occurs on js file: whproxy.js

function RegisterListener(framename, nMessageId) {

    var wSP = getStubPage();

    if (wSP && wSP != this) {

        //return wSP.RegisterListener(framename, nMessageId);

    }

    else {

        return false;

    }

}

So I commented it out to avoid the error being thrown. What is the fix for this?