As previously announced, we plan on updating the AdWords API to prevent a subset of modifications to the NetworkSetting for existing campaigns. This change affects all existing AdWords API versions.

Display-only campaigns have been evolving over time, and have developed unique features which make switching these campaigns between Display-only and other campaign types (Search-only or Search-and-Display) unreliable. Today, these modifications can unintentionally change campaign behavior (for instance, disabling certain display-specific targeting), potentially causing confusion and negatively impacting the advertiser experience. So starting 17 October 2013, we'll begin returning a TargetError.TARGET_ERROR error for such NetworkSetting changes.

If you do not make use of the NetworkSetting to change the network for existing campaigns, this change will not affect you. All other NetworkSetting modifications will continue to behave as before. The table below outlines changes possible between campaign settings:

Current setting Setting can be changed to
Display Network Only Search Network Only Search and Display Networks
Display Network Only - No No
Search Network Only No - Yes
Search and Display Networks No Yes -

As always, please feel free to ask any questions on the AdWords API forum or our Google+ page.