Unable to copy file back from NAS drive

[muzznz]

I have a QNAP T219 P II. I backed up a users data to a directory the Shared volume on this drive.

Once backed up I rebuilt the user's laptop then went to copy the data back.

It all copied back fine except for 1 file, a 5.88 GB PST file. Whenever I try to copy this I receive an error message "There is a problem accessing \\nzaucnas1\shared. Make sure you are connected to the network and try again"

I can use the File station app to copy this file to a different directory on the Shared volume, but cannot copy It to any PC.

I have also tried to use a SUB stick, but they do not show up either in File Station or External Devices.