There might be various reasons for above error, but this case is very specific to a situation where SQL Server was installed on a machine which was in Workgroup whereas the backup destination was the server located in the domain. Here is the error message seen in SQL Agent job history. Let us learn about how to fix Operating system error 1326.
SQL SERVER – Migrating AlwaysOn Availability Group to New AD Domain
As a part of my independent consulting, I also provide a high level overview of the migration strategy. As a part of this engagement, my client wanted me to provide steps to move AlwaysOn availability group from DomainOld to DomainNew. This was happening because they were acquired by another company and they need to migrate all assets to a new domain.