I had to change my Google password and now can no longer get into Thunderbird.

Something worth trying is to remove your old password from TB via Settings --> Privacy & Security --> View Saved Passwords. Then hit the Get Messages button (little cloud with an arrow). TB should prompt you for your new password.

Thank you for your response, Joel. Unfortunately, I cannot open Thunderbird to get to my settings. The message I quoted in my request appears as soon as I click on the icon. My gmail account works perfectly, so I know the issue is not there. I think there is something in the Thunderbird/Google link that is sour. Bob

Is this an Oauth2 account, or POP3?

What is your operating system?

What is your default web browser?

Please show us a screen shot of the error message.

This error usually happens when cookies are not enabled in Thunderbird. The fix is to enable that setting (see <Settings | Privacy & Security | Web Content>) and make sure the "Accept cookies from sites" option is checked; also delete any cookies for Google/Gmail ( <Settings | Privacy & Security | Web Content | Accept cookies from sites | Show Cookies>.) ALSO, delete your currently saved passwords, as described above by Joel. Then restart Thunderbird and you should be prompted for your new credentials.

Of course, this depends on you being able to start Thunderbird so you can get at its settings. That's why I want to see a screen shot. You're describing the browser window that normally pops up during Oauth2 authorization so you can input your credentials, but I've never seen such a window that you can't either dismiss or move aside.