Have you seen the following error message when trying to log in?
"Welcome! You're signed in to Google Accounts under the email [your email address] and your Google Account password, but this is not a valid AdSense login."
Here’s some clarification and tips for troubleshooting:
If you’re seeing this error message, this means your AdSense account shares the same login and password as a Google Account, but the two accounts are not linked. As a result, when you try logging in at www.google.com/adsense, our system will only grant you access to your Google Account -- not your AdSense account. To resolve this issue, you’ll need to maintain two separate passwords.
The easiest way to proceed is to first ensure that you're logged out of Google Accounts for any other products you use, such as Gmail or AdWords. Then, change your AdSense password at https://www.google.com/adsense/assistlogin. You’ll be asked to submit your login email address to us, and we’ll then send a reset link to that address. When changing your AdSense password, please be sure to select a unique password that you’re not using with any other Google product. After you've changed your AdSense password, please try logging in again at www.google.com/adsense. [AdSense Blog]
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