I am not very sure you need to actually access the controls themselves. As I understand, you need to transfer some data from one page to another. This is a classical scenario for any web application.
If the data you need to transmit is simple and short, you can use query string; otherwise, you could use a post response.
The receiver of the data would check its request and would display the necessary data.
If transfer your data, you stay blissfully independent on the page that sends the data. Which is good, because you can modify the sender of the data as much as you want without having to modify it.
If absolutely must access the first page, do so with previous page property. Have in mind that when this page is accessed, ASP.NET re-creates the page with a limited life cycle, which in some occasions might lead to strange results.
the Telerik team