As it happens, the issue turned out to be with my own superadmin user account - I'm not sure why that would be. But creating a new account, or using a different account I ported over from the previous store worked fine in testing. More importantly, I finished populating the store and turned EShop on - and sold a product almost immediately.
The support I received in debugging this was above and beyond. Simply terrific.
__
a 'spit' is a rod upon which savory food was roasted, turned in ancient times by a worker called a 'jack', a middle English word for an ordinary laborer (eg jack of all trades, steeplejack, lumberjack). Today, this job is usually referred to as a 'pitmaster'.
