Symptoms
User Task associated form is empty and the task action header does not show up.
Diagnoses
I created the Document Review and Approval app using the tutorial. When an outstanding review or approval task is waiting to be completed and you try and open the form from the K2 Worklist, it does not render the form as it should (see attached screen shot) If you open the form directly from the link in the e-mail notification the form opens correctly.
Resolution
The User Task's form rules were not yet injected into the form re-deploying the workflow achieved this.