I have a number of *.mht files saved by IE8 which open correctly with IE8 but after installing IE9 I am unable to open these *.mht files to view the contents.
To solve the problem, I have uninstalled IE9 and *.mht files are now opened correctly by IE8 again. Until IE9 is able to provide the same functionality for *.mht files then I have no intention of upgrading to IE9.