Reverted Lollipop back to Kitkat - now I can't access the external SDCard
The permissions structures are dramatically different between Jelly Bean and KitKat, and KitKat and Lollipop. Upgrading allows it to recognize the older structure and alter it appropriately for the new needs. Going backwards affords no such ability, as the older version knows nothing of the newer one. Your best bet's likely going to be to copy all the data off of that card, format it in the phone, and then copy it back.