This error occurs when the access rights have been removed or changed. It's best to reach out to the Master Admin so they can check it and undo the changes made. Here's the link for more details: Add, delete, or change user access.
Also, we can perform some troubleshooting steps to see if this is just a browser-related error. The first one is by using an incognito window and log in from there. Here are some of the shortcut keys:
Google Chrome: Ctrl + Shift + N
Mozilla Firefox: Ctrl + Shift + P
Safari: Command + Option + P
You can also clear the browser's cache. These are the junk files that can cause errors when using QuickBooks Online. Lastly, make sure that the browser is updated or use a different one.
Post again here if you have more questions. Wishing you all the best!