Problem with event organization

Hi Everybody!

I'm trying to develop a new page inside my web application. The problem is that I think that I'm a little bit confuse with the event's flow.

First let's resume a little bit my conception :
I have a part of my .aspx page which contain user information. This part is inside an updatePanel.
Outside this UpdatePanel, I have a List box which contain the name of the users. I create a trigger for the UpdatePanel on the event "OnSelectedIndexChange" of this listbox. When I select a name in the listbox, the information inside the UpdatePanel change to concords with the user selected.

Also, during this trigger event, I create dynamically some textbox and label inside the UpdatePanel. The number depend on an information proper to each user. I also create a button that I register as a Trigger of the UpdatePanel. On this button click event, I try to access the Textboxs created in the "OnSelectedIndexChange&quo ...