I can't modify Security settings of OS After a reboot, I cannot configure my normal VPN connection, nor modify some Operating System security settings.

What can prevent me from making changes to security settings? Malware?
Applications which interfere with screen appearance can prevent a user from makes changes to security settings while the app is active.

The operating system has to be careful to prevent a 3rd-party application from having influence over security settings by changing the appearance of security options to the user. (best guess speculation)

A screen-color-changing app, Twilight, may have been active, and therefore, from a Security Manager's point of view, able to influence a user's input to system security settings menus.