Hi Ian,
Sorry to hear about your problems. This kind of situation typically appears when the Flight Logger - EHM server connection fails during part of the flight. In this case the appropriate ACARS don't reach the server, and this is the "missing information" the final error message refers to.
Unfortunately it's hard to tell, during the flight, when such a failure happens so it's not discovered until the end of the flight. As it is the same server that hosts the EHM web site, one way to check the connection is via this site: if pages load ok, then the connection is fine too.
Another rule of thumb is that the most important information are sent at takeoff, TOC, TOD and landing so it is a good idea to ensure the connection works at these moments.
For the next FL version a more robust approach was taken but as we talk about full rewrite, it's still far from beta...
Hope this helps
Andrei