Hi
The steps he is talking about is the controller.
The upgrade recommendations in the release notes for 6.3.1.13 states this:
For ArubaOS 3.x.versions earlier than ArubaOS 3.4.4.1, download the latest version of ArubaOS 3.4.5.x.
So you should have upgraded to 3.4.5 before going up to 6.3.x.x. The reason for this is that the AP's have flash partitions for the images, these partitions are usually expanded on newer releases to take into account future releases being bigger.
This is most likely your problem, too small partition for the new image.
You need to move the AP-85 to a different controller for upgrade or downgrade, unfortunately.
Roar Fossen