This one can be a bit tricky to figure out. Always check to make sure the GPO that you are working with is not disabled in some way. Sometimes GPOs are wholly disabled temporarily for testing purposes, and perhaps you forgot to turn it back on. It's more common that only half of the GPO has been disabled, and you are now wracking your brain trying to figure out why the new drive mapping you plugged in to your computer security policy is not working.

When creating a GPO, you will be inputting User Configuration settings, Computer Configuration settings, or a combination of both. If the GPO only contains one type of settings, you can easily disable the other side of the GPO so that when this GPO processes on the client computers, it does so more efficiently because the computer does not even have to look inside the unnecessary part of the GPO settings.

Whenever troubleshooting a GPO, remember to visit the Details tab and make sure you haven't set yourself up for failure by disabling Computer Configuration, User Configuration, or both:

Also remember that this GPO Status field follows the GPO wherever it goes. If you change a GPO to be Computer configuration settings disabled, all of the associated GPO links will also be set to Computer configuration settings disabled. Different links to the same GPO do not have individual filtering or status settings. If you make a change to one link, you are really making the change to the GPO itself. Therefore, your change affects every link associated with that GPO.