Recently I added protected my shared folders with guest password. But I have a problem, when I want to use ntbackup on another computer to backup my files to these shared folders, I have to connect to folder first using Windows Explorer and type guest password. Than it works, but I have to do it manually and my backup tasks are scheduled. The password must be typed once after starting the computer (connecting to my network) and before I shutdown my PC, the password saved so I don't have to type it and the tasks works. Is possible to use eg. command line at startup or schedule cmd to try to connect the network and remember the password.
You could create an account on the system you are backing up with the same name and password as the account that runs the backup. Give that account permission to access the folder you wish to backup.