I have the same problem, had a hdd problem and wasn't able the deactivate my last installation, probably forgot do deactivate other machines over the years and now I can't authorize my computer. If possible I would appreciate if all authorizations for my ID were cleared.
I also have this problem. I have contacted support through chat as suggested in other posts to this forum but the agent refused to help since she said chat is not available for free products. I need my authorizations reset. I'm not trying to subvert the DRM; I just want to test which way of reading would be most comfortable. This is making Adobe Digital Editions rather useless and I'm sorry that the public libraries seem to be locked in to using this software.
I believe that the forum was the remaining option ask for a reset of the authorizations, but after two week still haven't got a reply, which is unfortunate.