Prior to AMM 2.16.2, the Name field on the AMM’s Admin -> Users screen would allow for the entry of user names containing space characters. However, attempting to log in with a name containing a space character would cause the AMM to display an error stating “An invalid character  was present in the Cookie value” before completing the login process. To resolve this issue, navigate to the Admin->Users screen, remove the space from the user name, and save the user.
If a user logs into the AMM UI using HTTPS, then any subsequent login attempts on HTTP with the same browser will fail. The UI will not login, and instead just refresh. To resolve this issue, the user can clear their browser’s cache and cookies. Or they can simply switch back to using the HTTPS URL in their browser. For more information on how to clear your browser’s cache and cookies, ensure that the browser is open and selected, and then press Ctrl-Shift-Delete (Windows) or Command-Shift-Delete (Mac). If this doesn’t work, you may need to update your web browser to the latest version.