Thanks for the reply, Mcindus.
I've seen this issue with Windows 10 before... Try running FF8 from your first processor core only.
I've tried doing this, but the problem is, next time I run it, it goes back to "all processors", and I have no idea how to make it "stick". Since I have to rename the dll back, and then re-run the launcher, it will just go back to "all processors", and I get the same error (hence not being able to switch to single-core).
Also - check to see if your DirectX drivers are up to date. You might need to 'roll-back' your drivers. This seems to be a directx9 issue, mainly.
DirectX should be up-to-date already. I've run this installer:
https://www.microsoft.com/en-gb/download/details.aspx?id=35and according to the installer, I have the latest or newer version installed. I'm not sure how to roll-back to an older version, nor which version I should try using.
Also, make sure your prefs.txt has the cache set to 250 or lower.
It was set to 250, but after changing it to 100, I still got the same error.
Were you using Windows 10 before?
It was Jan 2016 according to my Steam achievement timestamp (I got the last achievement when I played most recently), so yes, I believe it was Windows 10.
It was a different system though (desktop). Right now I'm trying to run it on a laptop (don't have the desktop anymore).
Compatibility modes (win8 and win7) don't seem to solve it either.
Oh, and I forgot to mention this in my original post: I've turned off the steam overlay and cloud saves.