Hi, I'm having the exact same issue right now, did you manage to get it working? only the Avalonia version will actually run, other garage editor just doesnt load. then when I try to load a save I get that error.
Edit: Actually nevermind, I think anti virus blocked the download or something, worked the second try with it disabled.
So while we have a thread for GT5 regarding discussion on garage editors, we do not have one for GT6. And yes, thanks to Razerman, there actually is a save editor for GT6, it’s actually been around for almost 2 years now, but I don’t know if it’s even been shared here yet, so I figured it’s about time we finally get a thread about it.
I am aware we have a modding discussion here for GT6, but that one is primarily about modding the game data, this is about the save data.
Anyways, here’s the aforementioned garage editor for GT6:
1. Plug in your USB drive.
2. Go to Save Data Utility and find your GT6 save game.
3. Press Triangle on the save game and select "Copy".
4. Choose your USB drive and it will start copying.
5. If everything goes as it should, it should tell you it has finished.
Now I must confess, I have not used it much since I don’t play GT6 a whole lot, but it’s worked fine for me the times I have used it. As always though, if you have any issues, be sure to share them here so hopefully, they can be fixed later!
Something important I must mention is if you’re looking to do things like engine or chassis swaps, they won’t work simply because GT6 took measures in preventing these sort of things from happening. Such modifications were possible back when the game was online, but since it’s been offline, such modifications are no longer possible.
I reuploaded both of them to Google Drive with the creator's permission, and here they are. I've also added them to the OP.
GT6 Save Editor
GT6 Avalonia Save Editor