AOFO failure

We are running a job using AOFO with "Automatically select open file technology" . The job has been running fine for months, but recently some of the directories backed up by this job are failing with "directory could not be accessed" (the directories do exist).  We tested a standalone backup of one of the directories without AOFO and the backup runs successfully.  When we test with the same directory using AOFO on, the job issues a warning message from the Snapshot Provider (Veritas).  

Backup- Guide2.parkinsonsinstitute.orgV-79-57344-34093 - AOFO: Initialization failure on: "\\Guide2.parkinsonsinstitute.org\Clinic". Advanced Open File Option used: Veritas Storage Foundation for Windows (VSFW) and FlashSnap Option.Snapshot provider error (0xE000852D): Required module VxCMD.dll not found. Make sure that Veritas Storage Foundation for Windows (VSFW) is installed and that the system path includes the VSFW installation directory.Check the Windows Event Viewer for details.

We are not sure why this has started happening all of a sudden and to only a few files.  Any help would be greatly appreciated.

Thanks.