NULL Value??

Hi All, Im pulling my hair out over this one. I have an aspx page..when the page loads it need to choose to load 1 of 3 possible user controls....so it looks to a Session variable called ContentType. Once it knows the ContentType, It loads the correct control and stores what type of control to display in the cache. This works fine. now....after the user fills out the form, they submit it and I need to redisplay the page...this is where the problem is arising. When the page reloads...I check IsPostBack and if it is a post back....I read which control to display out of the cache and attempt to load it into the Placeholder control on the page. And here is the error that Im Getting: Value cannot be null. Parameter name: child Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ArgumentNullException: Val ...