Please ignore previous question - just me being slow: I've found them on the drop-down.

The one I was using ("http://timestamp.verisign.com/scripts/timstamp.dll") still failed today, but I switched at random to "http://timestamp.comodoca.com/authenticode" and now it compiles. (Odd though: I've been using SetupBuilder with that timestamp URL for well over a decade and never had this problem before.) Anyway, thanks again for your help.

Dave