I have exactly the same problem. I tried to reinstall OCS but without success. I tried to appy the solution marked as best answer in this topic, but only have a blank page after trying to login with my user/pw.
I managed to resolve this problem.
I was logging in with the wrong user, that's why the error was shown.
I remembered my ADMIN user password and everything worked fine.
so the right user was:
user : Admin
Good luck there.