Copied a file, gave it a new name with the same extension and now it says "can't be found"

So confused! I had some files created sitting in a folder and then needed to create copies and put them in a new folder

This was all fine until I then went in to open one of the copied files - I get the message say that the file...

"could not be found check the spelling of the file name, and verify that the location is correct"

I've tried shortening the names in case it was the character length but none are near the 208 character max. I've not changed the extension of the files or anything, all I did was change the name of the file.

Strange thing is, if I right click the file and then "Send To Mail Recipient" it will attach the file to an email and then allow me to open it from the email.

Anyone have any clues as to what's going on?
Thanks
Paul