What does this message mean? And how can I get around it?
Join Parcel, "Unconnected parcel groups will be split, try joining again."
I've noticed that error when there is a stray connection line generated inside the parcel that is not connected to anything but appears in the traverse grid.
I don't know the exact answer myself, but I did notice a thread where users experienced similar issues and had some suggested solutions:
Rejoin parcels - Land Records Meetup (Redlands, CA)| Meetup
Chris Donohue, GISP
I still haven't figured out how or why the connection lines I mentioned in my answer here and in the Meetup thread were generated.