Apr 04, 2012 04:27 AM|BU XI - MSFT|LINK
What the TabContainer does is to hold different parts of pages in a tabbed manner. All these content are in the same page, so when you try to use Response.Redirect, it may not be successful.
If you want to change to a new tab, and and the same time update the content in this tab, then consider UpdatePanel. After user signs in, trigger the UpdatePanel to update.