I have ASP.NET Web Application that contains MasterPage, ASPX Page where I load User Controls dynamically into UpdatePanel containing PlaceHolder based on menu selection. This w
Have you tried attaching the event in the Page_Init event instead of the Page_Load? This is how I do event assignment in my dynamic-control applications, haven't had any problems with that. Also, you mention this is being done in an UpdatePanel, is it in the content template? If so, are you adding appropriate triggers to it (If indeed you want this to happen in an AJAX manner)?
Are you setting the "autopostback" property to true?
Seeing some code would definitely help...
You need to re-create dynamic control on every single postback, remember the Page instance is created per request, if you do not re-create the control then it wont exist on PostBack.
Of course your control disappears, you didnt re-create it on the postback.
see here
Extract:
Dynamically added controls must be programmatically added to the Web page on each and every page visit. The best time to add these controls is during the initialization stage of the page life cycle, which occurs before the load view state stage. That is, we want to have the control hierarchy complete before the load view state stage arrives. For this reason, it is best to create an event handler for the Page class's Init event in your code-behind class, and add your dynamic controls there.