After migrating to a new file server, some files were no longer accessible even though ROBOCOPY copied them fine and reported no errors 😦
After research looks like 2012 now disables 8.3 file format by default and this can affect some older applications including Windows Explorer. Unfortunately ROBOCOPY is happy enough to copy the file regardless.
To enable 8.3 format on a volume d: use
Fsutil 8dot3name set d: 0
This will not however correct any broken files therefore needs to be in place before ROBOCOPY copies the files over. Not seen a way around this yet.
I have since found a /256 robocopy parameter that may help stop migrating broken files
Word of warning – Enabling this impacts the performance of the volume see here https://blogs.technet.microsoft.com/josebda/2012/11/13/windows-server-2012-file-server-tip-disable-8-3-naming-and-strip-those-short-names-too/