When someone says to clear your cookies or cache these are the steps you should be taking to do so. Avoid clearing all the cookies and cache for your entire browser.
Firstly. Try an Incognito browsing session. This already starts off with no cache, cookies, or session data for your browser. Note that if you had already started your session in the incognito browser that you'll have to close it entirely, all tabs and windows of Incognito, for it to reset.
If that doesn't work and it's been a recommendation for a problem where the known solution is to clear you cookies/cache...and not one...
Thanks Leo, I am always in chrome incognito mode and have used the same email for years. Its a bit of mystery why it gets an invalid message now. I hate to log in as a guest. I'll try the cookies etc.