How to complete factory reset w/o Google account info?

Iconianite

Factory reset of my A500 stalls, because login credentials to existing Google account are rejected as non-matching (though they definitely do!), and creation of a new account always fails in the last step with the message "Try a different user name. ^1 is not available". I never picked "^1" as user name, and the same error message appears when using any of the Google-suggested user names. So I can neither login to my existing Google account, nor create a new one to continue the installation process. Does anybody have an idea how to circumvent this dead end to finish the reinstall of Android?

Iconianite

Solved part 1: There is a choice to bypass Google account during Android setup, so I have a running 3.2.1 again. Still not able to link it to my Google account, can't install the Play Store app, can't upgrade to a newer browser, etc. etc.