When the Group Policy Management Console displays a blue exclamation mark next to an Organization Unit, it indicates that Block Inheritance has been enabled on the OU.

Block Inheritance on an OU prevents group policy from a parent container from being applied, unless the No Override option is set on the parent container.

NOTE: Local GPOs cannot specify the No Override nor the Block inheritance options.

NOTE: Right-click the OU to see that Block Inheritance is checked on the context menu. To toggle the setting, press Block Inheritance.