Just today my gmail on my 920 keeps asking me to update account info--ive entered username and password several times--it just keeps on popping up and asking again--all the while it still continues sync and show my new mails-- WTF!!
I wonder if that is more a gmail thing instead of a WP8 thing. The reason i say that is, I get the same message about twice a week on my WebOS phone. Yet, once I enter the pass its okay for a few days. Did you try a reboot?
i removed the account and readded it and now its normal again
no 2 step process
it was strange because all the time it kept asking me to update account details it still was syncing. In the settings section it showed that my google account "needs attention"