I tried out the first solution, but it still didn't work. I got the same error again.
I did try older versions of SB before posting here. But they were not compatible with windows 8.1. I got as far as installing it with compatibility mode, but after installation, SB just wouldn't open. So i uninstalled and went back to the latest version.
Just to provide more information, I can run the launcher and key in my login details. After that, the launcher closes, the game client opens for a split second and closes, then I get the error pop up.
I'm running windows 8.1
My core fiesta is installed on (D:) drive.
(Does the error have something to do with the game being installed in (D:) Drive?)
I think I'm gonna cry
Edit: It runs now. I went down the list of old versions and tried them one by one. 4.10 works for me.
Edit 2: Windows updated on my laptop, and now Sandboxie won't run. I'm back to square 1. -cries-