i had the same problem, i could login to the ASA using ACS and i went to enable mode using the local enable password, however, i somehow was no longer authenticated as the username i used, but my username shows enable_15, and i couldn't authorize any command, so i created a new user on the ACS (enable_15) and everything worked smoothly.
i don't think this is the solution, but it's working now.
i don't know why the username switches to enable_15, maybe because i am entering the enable secret which is local on the ASA
