"An item with the same key has already been added."

If this error message is shown from Vantage, it may be via Vantage itself or in Device Director. The issue usually stems from Vantage having more than one instance of a Workflow which have the exact same name. To check the workflow, log in to Device Director and find the problematic Vantage job. In the Job Details - the Profile being used is the same as the Workflow being run from the Vantage perspective.

To resolve the issue, it is necessary to delete all of the duplicate workflows, so that only one unique workflow remains. This will most likely need to be carried out by a Vantage expert.

"Index (Zero based) must be greater than or equal to zero and less than the size of the argument list."

When processing a job through Vantage, the above error will appear if there is an issue with the Vantage workflow name. You need to ensure that the profile name that Device Director is using for Vantage exists on Vantage and that the name on Vantage is unique.

"Object is not set to a reference of an object."

This error normally means there is a variable that has not been defined. It is a common error message, related to the error "Transcode Failed: Value cannot be null." which means roughly the same thing.