I read somewhere that the error detection rules on addon scenery had been relaxed in regards to errors contained within the scenery e.g. overlapping nodes etc.
Nowhere we ever said we relaxed anything. The program might be more robust, meaning it might *crash* less and will instead report MORE errors in the scenery, but that doesn't mean it will accept defective AFCADs, it will just try to catch more errors and log them cleanly without crashing.
I have just loaded a freeware LSGG and it didn't show up in GSX as a valid scenery and the log identifies it as containing errors.
When I opened the scenery in an editor there were numerous errors
As you can see, both GSX AND the editor ( I guess you used ADE, or AFX ), agrees on this scenery being faulty.
that on the face of it deliberate e.g. taxi lines with no connection to the taxiway network to provide what appears to be tarmac infill.
Using taxiways to fill up tarmac, when the BGL standard has a proper "apron polygon" command, which is way more flexible and doesn't have ANY effect on AI, ATC, etc, it's a very questionable method, doesn't make any sense (because there's already a proper way and better to do this), and we cannot support this.
To make this work will I have to in this case radically overhaul the scenery to remove the errors if I want GSX to work?
Apparently so. But not just for GSX: such scenery would cause issue with anything in FSX, from AI ground movements, to ATC, to 3rd party mapping and flight planning utilities, that will all end up confused by taxiways that are not really what they say they are.