Where do you store the data in EDS? It looks like you are (intentionally or
unintentionally) using an EDS backend which talks to Exchange.

If this is intentional, then we need to figure out what it complains about. Can
you run "syncevolution loglevel=4 --sync refresh-from-server memotoo calendar"
and then look at one specific, simple example that triggers the error? The
output should contain "generated" data that then gets sent to EDS. It'll be
interesting to see whether there is an empty email address involved.

If this is unintentional, then ordering of your calendars changed such that the
default calendar is no longer your local one. What does "syncevolution
--print-databases" say?

You can override the implicit default with
  syncevolution --configure database=... @default calendar