5 GB of free hard drive space may be your problem. General rule of thumb is to have more than 20% free space. Less than that and trouble starts to happen. Defrag will complain there is not enough free space, not even function, or the Page file may be having trouble, for example.
You may need to move data files over to an external hard drive, uninstall applications, clear Internet cache, clear temp files (Windows System and User), empty the Recycle Bin, etc.
When this is all done defrag the hard drive and try the install again. If the Page file is overly fragmented you may need to use an aftermarket defrag application to defrag it at reboot or may need a Windows IT person to look at things. Try PageDefrag from Microsoft Sysinternals.
You can also purchase a new hard drive and clone the current system volume over to it or reinstall the operating system. It is a good excuse to reinstall the OS and leave old problems behind.
Douglas Lauritsen, Autodesk Product SupportThank you for the follow up. I am glad you are up and working with Autodesk Revit 2011.
I bet you will find that your system works better with more free space on the System volume.
Douglas Lauritsen, Autodesk Product Support
We appreciate your quick feedback on this forum!