Windows ADK for Windows 8.1 is supported starting from build 6614
This article applies to:
Windows Assessment and Deployment Kit (Windows ADK) for Windows 8.1 (WinPE 5.0) is supported starting from Update 1 for Acronis True Image 2014 Build 6614 and higher.
You can see your current product build number in the menu Help -> About. If the number is less than 6614, select Help -> Check for updates to install the update. Alternatively, download and install the update from the Acronis Website.
See also Acronis True Image 2014.