Failed to start process for <any game>: OS Error 4294967260

[ticorj]

I can't start any game from Steam, although I can start them pertly fine directly from their folders under Library/Application Support/Steam.

Some games just don't start. Nothing happens. Others show the error "Failed to start process for <name of the game>: OS Error 4294967260"

Tried downloading other games. Tried completely removing steam and installing again. Tried clearing download cache. Nothing helped.

[ticorj]

Support helped me with this issue. It seems there was another user with exactly the same problem having the Cylance Antivirus installed. I didn't even know I had this antivirus installed, since my Mac was given to me by the company I work for.

Uninstalling Cylance antivirus solved the problem to me as well.

Hope other users can benefit from this solution as well.

[ticorj]

To uninstall the CylancePROTECT Agent on a macOS-based system, use the Applications > Cylance > Uninstall CylancePROTECT.app program or the command line (Terminal).

Command Line, Without Password
sudo /Applications/Cylance/Uninstall\ CylancePROTECT.app/Contents/MacOS/Uninstall/ CylancePROTECT

Command Line, With Password
sudo /Applications/Cylance/Uninstall\ CylancePROTECT.app/Contents/MacOS/Uninstall/ CylancePROTECT --password=thisismypassword

====
I had to restart my Mac in SAFE MODE to be able to uninstall Cylance since I DIDN'T HAVE THE PASSWORD:
====

Command Line, Forgotten Password
1. Stop the service
sudo launchctl unload /Library/LaunchDaemons/com.cylance.agent_service.plist

(If the Command Above fails even with SUDO, Try it again after restarting the Mac in Safe Mode by holding the shift key after the chime)

2. Delete the values.xml file
sudo rm /Library/Application\ Support/Cylance/Desktop/registry/LocalMachine/Software/Cylance/Desktop/values.xml
3. Re-run uninstaller
sudo /Applications/Cylance/Uninstall\ CylancePROTECT.app/Contents/MacOS/Uninstall/ CylancePROTECT

Command Line, Silent Uninstall
sudo /Applications/Cylance/Uninstall\ CylancePROTECT.app/Contents/MacOS/Uninstall/ CylancePROTECT --noui

[Mormegil]

I found an alternative to uninstalling. Just stopping the service temporarily is enough.

https://home-support.cylance.com/hc/en-us/articles/360012104813-How-to-Mac-Start-Stop-the-Cylance-Smart-Antivirus-Service

Hope it helps!