If you run The Witcher 3 and encounter a BEX64 error in this case you should disable antivirus / firewall that can block the game. If the problem persists, try the solution below.
You can try to delete the save files of The Witcher 3 from the folder «My Documents» making before backup files, and then try to run the game. Another solution: Start cmd.exe as an administrator and type in the command line “cmd”, enter the following command bcdedit.exe / set {current} nx AlwaysOff and press Enter.
If done correctly, you will see the message «The operation completed successfully.» If you get the message «Access Denied,» then you do not run cmd.exe as an administrator. Then restart your computer and after restarting, try to run the game.
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Are you insane? The firewall and antivirus are running _for a bloody good reason_