???hmmm,
The hard and fast way i find of sorting this issue is to fo into control panel, add and remove programs, uninstall IE8 'thus rolling it back to 7 or 6' and then reinstalling 8 from the microsoft IE8 website.
This is not my preffered method of solving these issues as you don't get to the root cause, but if time is an issue then it generally sorts out the problem.