associate list to workflow and use the list column from this workflow

Question

I'm using SharePoint designer 2010,

I have create Task List and I add to this list new field (field name: Reminder Date, Filed type:Date and time).

I have create Reusable Workflow (Workflow name: Task Reminder).

I save and publish the workflow, and then I Associate the workflow to the list.

now I want to edit the workflow, so I add the "Set Field in Current Item" action.

a. when I try to configure this action I do not see the associate list field.

b. from the workflow setting page I do not see the associated list.

where I make a mistake?