What if you can't install Powershell?

Having successfully installed Powershell on XP and Windows Server 2003 I wasn't anticipating any problems with Vista. Sigh! I've been in IT long enough to know better!

The Vista installation package comes in the form of a Windows Installer update package rather than a stand alone .EXE file. On launching this file everything seemed to go well until the message "Windows was unable to install this update" appeared. Hmmm, time to look at the log files.

Windows Update helpfully records all of its activites in a log file called 'WindowsUpdate.log' that lives in your Windows directory. Looking through the file I could see the install starting and then failing with the error 'Windows failed to install the following update with error 0x80070020: Update for Windows (KB928439).' Googling this revealed an MS Knowledge Base article that pointed to my anti-virus software as the culprit. Sure enough disabling my Bitdefender AV allowed the install to complete and I'm now happily running Powershell on Vista :-)