Hi,
I had the same problem, here’s how I solved it. WordPress’ instructions are incomplete:
1) The owner of that API Key (ivanmh) is not on the access list for this blog. When this blog was registered, (portorreal)’s API key was used. To add you to the access list, (portorreal) must visit this blog’s stats dashboard page and use the form at the bottom of that page…
2) Once (portorreal) add (ivanmh) to the access list, (portorreal) must upgrade (ivanmh) as administrator.
3) Then (ivanmh) should go and activate the plug in and enter his api key. There will be no “error” messages anymore.
4) the final step should be to ask (portorreal) to visit the blog’s stats dashboard page once again and click on the “leave the blog” icon. That should do it…
