Hmmm, "maybe you have error-message blindness, like a lot of people who just click away errors without reading them?" >> You are right.
I think my eyes completely skipped the 1 important keyword "... change the 'Preview browser' setting in project properties to another browser."
I spent all my time instinctively tinkering with C2's browser settings.
Will have to read error messages with more focus next time.
Thanks Ashley and sorry about the needless intervention.