It looks like he does have the permissions, He said the buttons never lit up for him, so I think he has them.
It seems that the buttons are very patient and will quietly wait till the list is refreshed before they light. If you close/open the window as soon as it starts to refresh, it bops them on the head so they get to work.
Yes, this is what i have to do every time. I wait for the list to start changing as it goes from the previous battle status to the new form. I then immediately close the interface and re-open it in order to get the register button to lite up. If i do not close the interface, and instead just stare at it, the button will never lite.
Note: I also have to do this to enter seige. When the message scrolls about seige starting, if I open the guild interface, enter battle is not lit. I have to close the interface and re-open it to lite the button.
Just another one of those things i guess.