Hmm! The actual wording of the error Description will give a clue as
to why the file can't be opened. Does the 'other network environment'
require permissions, OR is the file in use by other user[s]?


Nobody is accessing the files in my folder except me. I even
loaded my folder in explorer, left-clicked in my folder, selected
"New-Microsoft Word Document", and named the file as "whatever.docx".
Then I changed my VBA code to open "whatever.docx" and still got the RT
error 5457.


Note that closing the file in Word does not necessarily release the edit
lock on the file; - it may be necessary to close the using instance as
well!

Did you try opening with the ReadOnly arg set to 'True'?


I haven't tried ReadOnly as True yet. I'll try tomorrow and see how it
goes. I assumed it does read only by default, but I hope I'm wrong.