Article ID: 2688285 - View products that this article applies to.
When you clear the Enable PXE support for clients option on the PXE tab in the properties of a System Center 2012 Configuration Manager Distribution Point, the Apply button is unavailable.
To work around this problem, make a change to another option. For example, clear the All this distribution point to respond to incoming requests check box, and then click Apply.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.