Hi Bob,
The only thing I know that causes this error is if the current user is null when it tries to save. And the only thing I know that can cause that is if you changed the user email account or user name from one browser but had another browser where the user was still logged in with a persistent cookie under the old name. So the cookie says you are authenticated and have permissions but since it no longer matches your user the user is null and causes this error.
The solution is to log out and log in again so your cookie matches the user, then you should be able to save with no errors.
Hope it helps,
Joe