This is still an issue that has gone unresolved for over a month. I have 2 blogs and both are external to WordPress.com. Blog 1 - WordPress.com Stats work fine and I really like it. Blog 2 - I get the following error when I enter my API key.
Error from last API Key attempt:
The owner of that API Key (l********) is not on the access list for this blog. When this blog was registered, 's API key was used. To add you to the access list, must visit this blog's stats dashboard page and use the form at the bottom of that page.
The WordPress.com Stats Plugin is not working because it needs to be linked to a WordPress.com account.
Enter your WordPress.com API key to link this blog to your WordPress.com account. Be sure to use your own API key! Using any other key will lock you out of your stats. (Get your key here.)
How do I link blog 2 to my WordPress.com account as in the error message?