This morning, on first attempting to connect to gmail using Chrome 18.104.22.168, I began experiencing this message:
You have been signed out of this account.
This may have happened automatically because another user signed in from the same browser. To continue using this account, you will need to sign in again. This is done to protect your account and ensure the privacy of information.
Upon clicking okay, I was immediately logged out of my account. Clearing cache worked to log in once, but the problem recurred upon subsequent log out-log in cycles. Per this thread at Google support, the answer was to start gmail in “safe mode” with labs disabled using this url:
From there, I went into settings and turned off the “Super Stars” lab, though other users have reported the problem from other labs as well.
Update: The problem recurred, even with “Super Stars” turned off, so I disabled all Labs.