I might have a workaround, unless your use-case requires log-in via RPC for some reason. An important point to note is - logging in via RPC is supported only for 7-mode systems. Are you running a 7-mode or Clustered ONTAP?
If you don't need to log-in via RPC, run the command as `Connect-NaController yourController.yourDomain -Credential yourLogInUserName` and enter the password in the credentials dialog box when prompted. That should work without loading the ntapadmin64.dll.
If you're trying to script the commands, and want to avoid being prompted for password, you can run Add-NaCredential beforehand to store the credentials.
Or you can create a credential object in your script as
It might be a Windows-2016 problem - I remember there were some bugs reported on other cmdlets that perform disk operations (like the VM Conversion cmdlets), but nothing specific on Mount-NaController.
Would it be possible to try it out on an older version of Windows, with the changed authentication mechanism?
Following your last request i found out that our old servers (Server 2012R2) still run with version 4.1.0 of the Powershell Toolkit. With that I had some troubles using the credential authentication method so I tryed to update these servers to version 4.4.0 and there it was: The same DLL error as on our new 2016 servers.
Since the old servers are still productive I didn't bother to test if the credential authentication method and the mounting command work. I rolled back to version 4.1.0 as fast as possible.
After that I changed the version of the powershell toolkit on our new Windows Server 2016 Machines from 4.4.0 to 4.1.0. After that all of our scripts (using the rpc authentication method) started working again.
So my conclusion is that there are some bugs in verstion 4.4.0 of the toolkit. I can't say if the mounting problem is a new bug or if its related to the authentication method.