jQuery error (frontend.js): $link.on is not a function

I installed the ‘Ecwid Ecommerce Shopping Cart’ plugin and am getting a jQuery error: in frontend.js: ‘$link.on is not a function’ and my WordPress drop-down menus don’t work any more.

I found that if I comment out in frontend.js:

        $link.on('click', function() {
            if (typeof Ecwid == 'undefined') {
                return true;
            }

my drop down menus are appearing again – is there any native fix for this since this looks like a simple coding error of something that is not defined (‘$link’) in frontend.js.

Any help would be greatly appreciated.