The Google Adwords API team has a blog post entitled Version 3 Shutdown Today which states

Please take note… per our announcement on May 12, we will shutdown Version 3 of the API today.

Please make sure you have migrated your applications to Version 4 in order to ensure uninterrupted service. You can find more information about Version 4 (including the release notes) at

-- Rohit Dhawan, Product Manager

This is in compliance with the Adwords API versioning policy which states that once a new version of the WSDL for the Adwords API Web service is shipped, the old Web service end point stops being supported 2 months later. That's gangsta.

Thanks to Mark Baker for the link.