Duplicate jobs fail with log message : Duplicate Failed (4043456)

Symptoms:
Scheduled duplicate jobs fail with the error message : Duplicate Failed
[NetVault | Job Management] contains a list of phase 2 jobs when the corresponding phase1/backup has yet to run.

Scheduler warning message listed within NetVault log as:
Job XX Phase 2 not run, A previous instance is still active

Description:
The duplicate job is scheduled when the phase 1 part of the job is completed.
Hence, each time you run a backup job with the Duplicate option, a new duplicate job is scheduled with its own duplicate schedule specified in the Advanced Options tab.

If you have a duplicate schedule defined with the repeating option enabled, then each time you run the backup job, a series of duplicate jobs will be scheduled (in accordance with the repeating schedule option defined).

I.e. if you have a duplicate schedule that defines a job to be run at 23:00 every night of the week - if you run the backup job once and the phase 1 completes sucessfully, then there will a duplicate scheduled for evety night of the week .

The first time the job is run both backup and duplicate will work.

However when you run the backup job on the next night another series of duplicate jobs will schedules at 23:00 each night.
This will cause a conflict in the scheduler as you can only run single instance of a job at any point in time.

This duplicate schedule requests that the scheduler executes 2 instances of the same job at the same time and the scheduler fails both of them with the error message:
Job Status: Duplicate Failed.

Therefore the only legal options to select when creating the schedule set for the phase 2 duplicate are Immediate or Once.

Edit the duplicate schedule sets and set the option to once.
Edit the policies (when in use ) and ensure the correct Advanced Options sets are being used for the duplicate jobs.