Ah, ok - I will poke around there. I haven't changed any code so not sure how that could have gotten messed up. But I have updated B4A and also Android Studio to the latest versions.
My main module has this at the top:
#AdditionalRes: ..\resource
#AdditionalRes: C:\Users\Dave61\Dropbox\Personal\B4A\AdditionalLibraries\b4a_appcompat, de.amberhome.objects.appcompat
#AdditionalRes: C:\Users\Dave61\Dropbox\Personal\B4A\AdditionalLibraries\b4a_floatingactionbutton, de.amberhome.objects.floatingactionbutton
#AdditionalRes: C:\Android\sdk1\extras\android\support\v7\appcompat\res, android.support.v7.appcompat
#AdditionalRes: C:\Android\sdk1\extras\android\support\design\res, android.support.design
#Extends: android.support.v7.app.AppCompatActivity
and I checked that all the folders mentioned there do actually exist....though I am not sure what the last parameter on each line means in regard to the directory. There is no file called de.amberhome.objects.appcompat in the C:\Users\Dave61\Dropbox\Personal\B4A\AdditionalLibraries\b4a_appcompat directory for example, just a Layout directory with 5 xml files.