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 know it is not an exact solution but using external drive paths solves this problem.

BACKUP DATABASE AcinsoftDB
TO DISK = 'E:\MyDB.Bak'
WITH FORMAT,
MEDIANAME = 'C_SQLServerBackups',
NAME = 'Full Backup of MyDB';