Thanks for your help Lainz,
Well this ended up being a very strange one.
I had to just scrap the whole previous installation.
I had not placed any new components for ages, and things seemed to have been running well right up to the time the BGRA components seemed to give trouble - but I don't think it was them as such.
Updating them in the Online Package Manager (OPM) then led to this problem (previous messages).
Ended up wiping the very directories, OPM directories - all settings - just everything.
Utterly clean install of everything appeared to be required, and then relocating and installing the few previous components not covered by the OPM (like CEF3).
IDE is fine now (as expected from a clean install).
Lazarus 1.8.4 r57972 FPC 3.0.4 x86_64-win64-win32/win64
Current project now reopens, compiles and runs successfully - now back to original reason for these BGRA posts :-)
Is there a way during install to go for a BigIDE full component set, just like Code Typhon (which I completely migrated away from quite a while ago)?
Paul