Could not open the file error message on Windows

Hello,
I am using Windows NT machine for my business purpose. I know this is quite an old OS but there are a few settings which I find very stable in Windows NT.
Everything was working fine, but from the past few days whenever I am trying to open any file or folder I keep getting this error message:

Couldn't open the file because the file was not open.
I do not want to upgrade my OS just for this particular error message. I was hoping if someone was aware of this error message.
I would appreciate the help if anyone could suggest me why I am getting this error message on my machine.
