Hello Gibbo, and welcome to Sysnative :)
Linked here is an article which details how to enable or disable verbose Windows Installer logging.
http://support.microsoft.com/kb/223300
I want you to:
1) Enable verbose Windows Installer logging (use the Fix-It at the above link)
2) Re-run Windows Update. Try to install any updates you are offered.
3) Download the KB update in question and try to install it manually:
Download Microsoft .NET Framework 4 (Web Installer) from Official Microsoft Download Center
4) Disable verbose Windows Installer logging using the matched pair Fix-It from the link I provided.
5) Run collect.exe and copy to Desktop, zip up & upload both
%temp%\vslogs.cab &
C:\Windows\Logs\CBS folder. See here for details:
Instructions to collect .NET Framework 4 and Visual Studio 2010 setup logs - VarunGupta - Site Home - MSDN Blogs
.net issues are sometimes quite difficult to fix. If it's Windows Installer store corruption we don't have a chance. If it's most other things a forced uninstall will do the trick - but we first need to check whether there's anything which could make the situation more complicated or unstable. In such a situation we have to attempt a fix, and it's a bit hit and miss as to whether your error will be fixable or not. Still, we'll hope for the best. With any luck the logfiles will reveal some useful information we can make use of.
Fingers crossed :)
Richard