Hi duckeyeis, I’m sorry to hear you’re having trouble accepting “The Equinox” from Fearghas Abernathy in Agartha. Are you able to see the mission icon before doing so, and have you had trouble accepting missions from any other mission providers, recently?
If you’ve had trouble accepting missions in general, it wouldn’t hurt to repair your game installation. You can find instructions for this here:
As Blodwedd said, you should also still be able to queue for an Occult Defence scenario at any time through the Activity Finder window (shift+v).