The 
CONVERSION DURATION THRESHOLD placeholder was deprecated on 
April 28th, 2014. Starting 
July 21st, 2014, using this placeholder with the 
FeedMappingService will result in a 
FeedMappingError.INVALID_PLACEHOLDER_FIELD error for all AdWords API versions.
See 
this post for details on how to set your conversion duration going forward with the 
CONVERSION TYPE ID placeholder instead.
If you have any questions about this upcoming change or anything else related to the AdWords API, please contact us on the 
AdWords API forum or via the Google Ads Developers 
Google+ page.
- Ray Tsang, AdWords API Team