I have ran into similar problem with watin on a site using Ajax. This is the workaround for this.
//After click on link/Tab/Button on which the result is loaded in non Ajax websites.
We have a function here, browser.WaitForComplete()
but it works only when the page is in loading state. but in case of Ajax on a part of browser window gets updated. so no loading state for browser.
So one solution for this problem is
Use Thread.Sleep(10000);
This time can vary upon the normal time the website takes to load the required div.