Starting on April 11, 2012 we will require the API version string to be included as part of the HTTP request when downloading the AdWords API 
AdHoc reports. If version is not provided, the RequestError.INVALID_INPUT error will be returned. The requests for downloading reports should be sent to the following URL,
https://adwords.google.com/api/adwords/reportdownload/v201109
If you are using the latest versions of our 
client libraries for downloading reports, this change will not affect you.
As always, please feel free to ask any questions regarding the AdWords API on our 
forum or during scheduled 
office hours.
 - Stan Grinberg, AdWords API Team
 - Stan Grinberg, AdWords API Team