We are having a issue with the backups on one of our 2012 R2 servers. After working fine since the server was installed over 6 months ago the scheduled backups now keeps on failing with an error of unable to write to backup target. We are using the built in windows server backup to preform a full backup including system state each night to a external drive. Once set the backup will usually work for several days then it will fail and the only way to get it working again is to wipe the drive delete the backup schedule and recreate. we have tried using a variety of different drives, different ports, drive letters, made sure the system is fully updated, and have tried using the backup to volume option and the back up to dedicated drive with in the backup settings.
Non of this appears to make any difference, it sill fails after several days....