IIRC some people here have had some issues w/the "E" version of the dongle, vs. the "P/Plus" version. I haven't followed it closely as I only have the Dongle P version. You might want to check the thread that @kkossev linked to see the discussion regarding the "E" version.
Actually maybe I'm remembering a non-issue. 
This post in the dongle flashing thread shows successful flashing and joining of an "E" version, and there is more info on the E version in the second post of the thread.
