When users are experiencing access issues, one possible solution could be to clear the browser cookies. Below are links to instructions for how to clear cookies in different browsers.
If you receive an error that says "Disallowed Key Characters", you should be able to fix this error by clearing your cookies in your browser or using a different browser. See the links below for instructions on how to clear cookies in different browsers.
Instructions on how to clear cookies in Chrome. 
Instructions for clearing cookies in Microsoft Edge
Instructions for clearing cookies in Firefox
Instructions for clearing cookies in Internet Explorer
Instructions for how to clear cookies in Safari
