I am now getting this same error. If you are a logged in member and try to suvscirbe, it give you the "Error occurred while subscribing" message. I you are not logged in, it will just hang and be unresponsive.
I am running the latest version of enewsletter.
The site having difficulty is http://offworldnetwork.thirdscribe.com
I have had mixed results with the widget, but the shortcode is definitely not working.