+1
I see the same issue using file:// and file:/// syntax,
ESMC 7.0.550.0
2018-07-13 14:54:52 Error: CSystemConnectorModule [Thread 22a4]: Software installation failed: boost::filesystem::status: (0x5), Access is denied: "file://\\vm-gb-srv\share\ees_nt64_ENU.msi"
The share is accessible via the local machine and has SYSTEM added in share and NTFS permissions.
It works fine with a local path.