For the first lesson in the BullCow Cartridge game, I compiled the sources which were unmodified everything compiled OK. I changed the BullCowCartridge class file (.cpp) to add the simple PrintLine(“Hi There!”) line and saved the file then compiled inside UE. I had compiler errors complaining of a mismatch in precompiled headers from the BullCow Cartridge project. I also compiled the BullCow Cartridge project from within VS 2019 and had similar errors. To remedy this I had to perform a complete clean from the build menu of VS2019. This then compiled correctly within UE.
just in case other people had similar problems.