I have confirmed the problem you are seeing with plate solves using the astrometry.net server. I am communicating with Dustin at asrtometry.net to work out what is going wrong. I'll report back when I know more.
If you happen to be using a Windows PC, try installing the local solver called ansvr. Detailed ansvr installtion instructions are here:
http://astroimagej.170.s1.nabble.com/AstroImageJ-3-2-0-Released-new-local-astrometry-net-server-supported-for-Windows-users-td338.htmlKaren