There has been alot of chatter around the new ADK for Windows 10 1703. Microsoft somehow signed a mountdriver with a bad certificate. This means mount operations fail. All around deployment father Michel Niehaus has found a workaround and you can read the full post from him here https://blogs.technet.microsoft.com/mniehaus/2017/05/16/quick-workaround-for-adk-1703-issue/
The short story is that you need to modify a registry value to use the built-in driver instead. So if you don’t want to read the full story change the following registry value
Set the value to
Then you can mount images again!
Note: There are people saying you can turn of SecureBoot to make it work and while this is true. You should not turn SecureBoot off.
Note 2: Microsoft is working on a fix for the ADK.