Cannot open backup device. Operating System error 5

Question

Below is the query that I am using to backup (create a .bak) my database.

However, whenever I run it, I always get this error message:

Answer 1

I experienced this problem when the .BAK file was temporarily stored in a folder encrypted with BitLocker. It retained the encryption after it was moved to a different folder.

The NETWORK SERVICE account was unable to decrypt the file and gave this thoroughly informative error message.

Removing BitLocker encryption (by unchecking "Encrypt contents to secure data" in the file properties) on the .BAK file resolved the issue.