The previous method of supporting AlwaysOn (via the registry option SkipChecks) is no longer available.

You can use SQL Backup Pro to back up AlwaysOn Availability Groups, including taking a backup from a ReadOnly secondary replica.

You can use any of the following options:

For additional file name options see File location tags

For more information about the types of backup allowed on Availability Group primary and secondary replicas, see AlwaysOn Availability Groups (SQL Server) and Configure Backup on Availability Replicas (SQL Server) on MSDN.