I've had this issue as long as I can remember – Adwords and Google accounts collide. If you are an intense user of both, you know what I'm talking about.
It is a great mystery why Google invests so much money in developing magnificent products that generate 0 revenue, and the one product that brings in all of its revenue – adWords – remains a step child. It is the only product that works really badly with the whole Google single-signon system. To take just one small example – the password strength requirement is different in AdWords. AdWords requires a stronger password, so if you attempt to sign up for a new Adwords account, your good ol' password from your Google account may not be strong enough.
Anyways, that's enough whining for one post. The reason I'm writing it is to explain how I finally got all my logins lined up without getting thrown from one account to another unexpectedly or getting logged out in the middle of writing an email.