so I spent the last 3 hours trouble shooting why I was unable to get Tree of Savior to start. I went through every, “solution” that I could find and nothing would let me get past this error message. It wasn’t until my GF informed me of a message she got when she launched this game, “uninstalling ToS (tales of symphonia) files”… so it turns out a modded patch I installed for Tales of Symphonia was interferring with the start up of the game!! so after skimming through a bunch of old threads I found the fix to remove the patch manually.
you can access the HKEY_LOCAL_MACHINE\ by going to Run: and typing “regedit.exe” (please be careful in the registry, you can 
things up!!)
Complete Manual Uninstall (applies to versions older than 0.6.3)
If tsfix_enabler.exe does not successfully uninstall, you can manually remove the mod from your system by deleting the following registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\TOS.exe
Finally, delete d3d9.dll from %TEMP%
hopefully this can fix the issue for you guys still unable to get on! as for me, im off to test this game out now o/
(I posted this on the steam discussions yesterday and was asked by users to put it up here as well just incase anyone has missed my solution)