Error System 5 Access is denied. (ExecuteProgram) reported during the backup process.
When performing VSS-Aware backup set, Asigra will call MS Volume Shadow Copy Service that running on the source machine to take snapshot, while at the same time if you have another Volume shadow provider such as Hyper-V Volume shadow provider running on the same server, there is a chance that these two vss providers conflict and cause the problem in this case.
Disable the other provide(s) that conflict with MS VSS provider.
Refer to the AssureStor Knowledgebase for how to disable unwanted VSS provider.