When trying to mount the Windows 10 Enterprise x64 build 9879 ISO in File Explorer, you may get the following error:
Couldn’t Mount File, Sorry, there was a problem mounting the file.
This is a known issue when the sparse file attribute (P) is set on the file (9879.0.141103-1722.FBL_RELEASE_CLIENTENTERPRISE_VOL_X64FRE_en-us.ISO).
To make it work, simply make a copy of the ISO, or remove the sparse file attribute from it. Here is a link to a PowerShell function that removes the attribute: http://superuser.com/questions/818303/how-to-mount-an-iso-image-that-windows-8-1-refuses-to-mount
You can check the attribute by viewing the file properties (Details), or by running the following powershell command:
Checking attributes in PowerShell.
Checking attributes in File Explorer.