Using Zombie with ASP.Net postbacks

We are trying to set up some load testing of an app written in ASP.net, that makes extensive use of postbacks to change the screen content after clicking submit or a link. We are having some success, but I have a button that is not showing up in Zombie, and that is added via postback. I have tried pressButton and clickLink on it. It's a submit button, with the text Next, and a long ASP.net field name. But the error keeps coming back that it doesn't exist. Is it because it was created by the postback, and can't be found by zombie?