Apr 06, 2012 08:48 PM|Digitborn.com|LINK
Further investigation and testing showed up that the ClientID is different for the same control:
on: XP, IIS 5.1 it's 'ContentPlaceHolder1_Tabs_TabPanel1_up2'
on: Server 2008, IIS 7 it's 'ctl00_ContentPlaceHolder1_Tabs_TabPanel1_up2'
on: ASP.NET Development Server it's 'ctl00_ContentPlaceHolder1_Tabs_TabPanel1_up2'