Fixes 'hidden content' within the tab control in IE8 and earlier for ASP.NET 4.0
If your site uses the ASP.NET AjaxToolKit, you may have noticed or received reports that sections within the tab control have their content hidden on older browsers. Specifically, this seems to affect IE8, IE7, IE6. Versions of Internet Explorer from 9 onwards are not affected, neither are other browser types such as Google Chrome, Mozilla Firefox and Opera.
The issue is due to a bug in the source code for the AjaxToolKit. Fortunately, although it's a Microsoft project, it is open source, and the source code is freely available from Codeplex. Using information about the bug, and how to fix it, from other users on Codeplex, we downloaded the source code, fixed it, and compiled our own AjaxToolKit DLL.
Just in case you're having the same problems, and you're looking for the latest (as of 30th April 2013) AjaxToolKit but with this fix incorporated, here is the file:
DOWNLOAD - AjaxControlToolkit_fixed_for_ASP.NET_4.0.zip (1.64 MB)
You just need to download this file, unzip the DLL and replace the existing file of the same name in your site's /Bin folder. Note that this is the latest AjaxToolKit code as of today (30th April 2013), so it may break functionality if you use it with ASP.NET projects designed to use older versions of the AjaxToolKit. You must back up the old DLL in order to restore it if you find this new DLL breaks anything.
DISCLAIMER: this code is offered 'as is', for free, without any warranty or support. Use entirely at your own risk.