I am trying to create a reusable workflow and I want gather information from a task that was created by the workflow.  Because the workflow, once added to a library, allows selection of the task list, I need a way to find the task no matter which list.

There is an value in the Lookup details > source dropdown labeled "Association: Task List".  I am assuming that this should be the list that was selected.  However, when I select that value, I am immediately presented with the following error.

It doesn't matter which site I'm in, it's always the same except with a different GUID.