I deactivated an old authorisation that was giving me trouble.
Did you deactive on the Adobe site, or deactivate it from your copy of ADE?
If you just deactivated it on the Adobe web site, you need to deactivate it from ADE as well.
As long as ADE does not close itself after giving you that (typically unhelpful) error message, enter ctrl-shift-D to ADE (cmd-shift-D if on a Mac).
Restart ADE, and you should be able to active/authorize with your new ID.
If that is not appropriate/doesn't work, please ask again.