1. Locate the Startup Account for your SQL Server service
  2. Right click on the folder to which the backups are being created and select Properties
  3. On the Security tab verify that the user from Step 1 has Full NTFS permissions to this folder or add these permissions if the user is not listed.
If the issue persists after completing the above, then please perform the following steps:
  1. Detach the database and select to remove all existing jobs for the database.
  2. Reattach the database
  3. Recreate the automatic removal of old files