So last night I shut down the MacBook. Powered up this morning, and reconnected to the external HD as TM was trying to get its feet under it. TM stopped its attempted save, waited 90 seconds, then started up again, connecting to the external HD without a hitch. They’ve resumed playing together just like they’re supposed to.
I know you’ve all been waiting for news with collective breath bated, so I thought I’d let you know.