This error usually occurs when prototype js library is not loaded and that leads me to believe its some sort of server config issue and some of the JS libraries are not loading correctly! With firebug or a similar tool, you should be able to find what those libs are. You can also look at the generated HTML source on portal page to confirm the libs pointing to right presto server. Look for html fragment under the following comment for portlet content.
<!-- Mashlet container div -->



I have successfully installed the presto-liferay connector war file into a Liferay 5.2.3 server. When I select the 'preferences' portlet option to bring up the Presto service/mashlet selection, I see a swirly processing circle, but nothing else.
In Firebug, I see the following errors:
Class.create is not a function
http://xxx:8080/presto-liferay/mashletconfig-1.0.js
Line 86
Presto.Portlet.Config.MashletConfigWidget is not a constructor
http://xxx:8080/web/guest/page-bus?p_p_id=JackBePrestoMashlets_WAR_prest...
Line 14
I have updated the portlet.xml to set the Presto server in the there with the appropriate URL. Is there something else I am missing? I also tried the jquery fix mentioned here.
TIA,
Lou