Question_Agile Process_ UIE Virtual Seminar

Hello Everyone...

I am referring to the model that is given in
UIE Virtual Seminar
The Essentials of Agile Development that is given by Jeff recently...
(SLIDE 30)

We are already working on this model but we have an issue.

Scenario: Assuming that we have six features to a project and business
and the designer will be working on "First feature" in Iteration ZERO
with the Requirements/ Screens / Spec for three weeks and they are done
with it. (in Iteration ZERO developers may not be ready to participate
with designer as they will work on some other technical tasks)

Once we move on to SECOND Iteration and we will give Requirements /
Screens / Spec of the First feature to the developers so that they can
code it..   and this is where the problem comes

Problem: If there is a technical problem/Limitation that arises for the
designs that we already worked on ITERATION ZERO how do we handle it?

-laksinu