I uninstalled it and reinstalled it and seems to work fine now. Apparently one of the two update patches I downloaded screwed it up. Or I screwed up the process somehow.
Anyway, nothing like a purge. Will not mess with the online updates, at least until I reexamine them closely and get daring again.
During installation the game is a little funny about telling you to install disk 2, then complain it needs disk 1, then reject that and demand 2 again.
Come to think of it, in previous installation, after I installed disks 1 through 3 (IL-2, Forgotten Battles, Expansion Pack), the game used to want disk 2 before it would play; now it wants disk 3.
Oh well. Will enjoy it as it works now.