In Windows Explorer the UNC long path construction errors out as:
Windows cannot access \\?\UNC\server\share
(Error: 0x80004005)
Background: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
To specify an extended-length path, use the "\\?\" prefix. For example, "\\?\D:\very long path".
The "\\?\" prefix can also be used with paths constructed according to the universal naming convention (UNC). To specify such a path using UNC, use the "\\?\UNC\" prefix. For example, "\\?\UNC\server\share", where"server" is the name of the computer and "share" is the name of the shared folder.
What am I missing here? The UNC prefix never worked for me.