[horde] No synckey could be found.

[Simon B]

Hi Michael

After upgrading to ActiveSyng 2.10.1 I noticed this in the activesync
log for my device on the production server (I still can't get it to
work on the git install).

2014-01-13T12:50:43+00:00 ERR: [21881] Attempting to add a collection
                    to the sync cache while requiring a synckey, but no
                    synckey could be found. Most likely a client error in
                    requesting a collection during PING before it has issued a
                    SYNC.

What does this mean?  And any idea how to fix it?

Thanks.