I was facing this error in one of my servers while trying to open gpedit, with additional message “The volume for a file has been externally altered so that the opened file is no longer valid”.
Here is how I fixed it.
1) Enable view hidden files from explorer.
2) Navigate to C:\Windows\System32\GroupPolicy\Machine
3)Rename the file Registry.pol to something else.
4) Run gpupdate
By now, I was able to open gpedit normally.