I'm using windows 7, service pack 1. But I had a problem running the 64-bit client after the patch. The 32-bit client works normally.
So I've tried a few methods like reinstalling updates for windows, completing the optional updates, and other stuff, till I tested this one. I hope it helps someone else.
Keyword: Compatibility
Right Click Blade & Soul Desktop Shortcut
Properties
Compatibility
Compatibility Mode
Check "Run this program in compatibility mode for:"
Choose Windows XP (Service Pack 3)
Apply & Run the Game
For windows 10 users, if you're having a problem showing older versions of windows, please run the compatibility troubleshooter as shown in this article
Looks like changing the compatibility affects the game greatly, here are my results for 64-bit client: 64-bit
Windows 95
Windows 98/ Windows ME
Windows NT 4.0 (Service Pack 5)
Game fails to launch.
Windows 2000
Windows XP (Service Pack 2)
Windows XP (Service Pack 3)
Fast game start up time
Fast loading screen
Stable FPS all the time
Windows Server 2003 (Service Pack 1)
Windows Server 2008 (Service Pack 1)
Very slow game start up time
Very slow loading screen
Very low FPS all the time
Windows Vista
Service Pack 1 Error
Windows Vista (Service Pack 1)
Windows Vista (Service Pack 2)
Slow game start up time
Slow loading screen
Low FPS all the time
Windows 7
Service Pack 1 Error