AdWords Editor Error Number: 211

Added some new AdGroups and Keywords to one of my AdWords Campaigns today and when trying to upload them kept getting the error: Post changes encountered a fatal error AdWords Editor received an error from AdWords that it does not recognize. This probably means that the version of AdWords Editor that you are running is out-of-date; please check to see if a new version is now available. (Error number: 211) Looking around I found the [...]