How do you remove the invalid system task? I put a ticket in this morning and haven't heard anything back yet.
The support specialist set up a webex and ran a custom SQL task on the Tableau application database. Unfortunately it's not something I could replicate. Additionally, they mentioned there are a few things that could cause this, so I'm not sure if the steps taken in my case would be helpful in all cases.
If you haven't already, one thing I'd recommend when submitting a ticket is to include recent logs. Instructions on how to zip logs into one file are here:
Creating Tableau Server log files
Then you can just attach them to your ticket.
Looks like Tableau is officially fixing this in 8.1.1 (http://www.tableausoftware.com/support/releases/811)
Not sure how this helps those of you currently stuck, but I thought I would add this info to the thread.