This is a common error when you're already signed into a personal gmail account. Instead of logging out of your personal account, you can open an Incognito Window on Google Chrome or Private Window in Safari/Microsoft Edge/FireFox to access the form: https://sites.google.com/berkeley.edu/alumni-email/home
You should then be asked to login with a Google account in which you'll use your @berkeley.edu account (not @cal.berkeley.edu or any other alias). Then you should be prompted to authenticate with CalNet ID and passphrase to proceed to where you can submit your alumni email renewal form.