I was trying to take the backup from GUI

When i selected the path the error i am getting is "can not verify the existence of the backup location do you want to use backup location anyway"

i selected yes once after this when i clicked on ok the error i getting is

can not open Backup device '--------.trn' failed to create. Operating system error 1326(Logon failure: unknown user name or bad password.). [Policy: MSSQL Logfile Template]