Thanks all for the attempts to help.
Just had a session on the phone, wasn't able to resolve it yet - I think it'll have to wait until I can get there in person.
Some more detail though (and corrections): the error does not come up in a loop, just once each time you start up iPhoto; the iPhoto window shows one photo (and what I guess is a thumbnail) and the title bar shows a URL for Facebook. (Supposedly unplugging the router disabled internet access without changing the iPhoto behaviour, but clicking on the URL still opened FB in a browser window, so I have suspicions about the information ...)
Once I can get in front of it and see what happens for some random clickery, I suspect it'll be straightforward to fix.