I was having issues getting tasks to execute consistently on our PDM archive server. In the end it was because of a conflict in user name, and who was logged in.
On the task, I correctly set it to execute as admin:
However, when I was remotely connected to the server, I was logged in using my windows username and id....ie corey.hinman.
So the task was to execute as Admin, but the vault was logged into as corey.hinman. I turned off automatic login based on current user id, and logged in as Admin. Tasks are now running nice and smooth.