Checked that antivirus isn't causing the problem - it's not. Nothing quarantined and realtime shield temporarily disabled. Same issue with 10.6. I can no longer check versions before 10 as I deleted them after downloading 10.5.
This issue has since resolved itself. I tried the game very recently and it runs fine now. I expect the problem happened because of an nVidia driver at the time that had some compatibility features missing. Apart from some small Windows updates, everything else is still the same.
