Editing the “default task form”

I'm trying to add a couple of fields to the “default task form” in outlook 2010. We also use exchange server.

I enable the developer tab.

I choose “ Design a Form”

I pick "Task" from the Standard Forms Library.

No problem ….. Right!

The “Tools” and “Arrange” blocks are greyed out on the ribbon. I can’t select, add or delete anything from the standard form. Basically, I can't edit the form.  How do I go about editing this form?

Any thoughts??