Access errors on google usually resort from students logged into a personal google account even though they think they are logged into their GCPS google account. You can verify which account the particular link is defaulting to, but clicking on the initial in the top right corner of the tab.
If it is any other account besides your GCPS account, click “Sign Out” and then return to student portal to access your account.
If the problem persists, please click the initial at the top right again and chose “Manage Account”. In the search bar, type in “Cache” and click clear all browsing history. This should solve the issue.