This error occurs when the directory selected by the generic backup file is the disk root or the backup selected partition does not grant the SQL Server user read and write permissions.
The solution is to grant SQL Server users permission:
Select the folder that you want to back up, right--and secure--see if the "group or user" contains the Authenticated users name, because it is included in all authenticated accounts on the computer or in the Active Directory. If there is a read-write permission assigned to it, do not click-and-edit-add---find this user after you add, and then assign permissions to it, (note: Use this user to assign permissions when you log on to a SQL Server server with Windows identity , add "group or user name" If other login method is used)
"Operating system error 5 (Access denied)" occurred while backing up the SQL Server database. BACKUP DATABASE is terminating abnormally. "The Wrong Solution