Just thought I would pass this along since I did not find this fix when I google it.
I had a person who had problems with windows xp and internet explorer 8, going to sites like target and payal it would say problems viewing the site. After checking google I found that it had to be something with user agent.
I found that the key in the registry
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\User Agent\Post Platform]
"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1) "="
Was causing the problem I deleted it and it fixed the problem I also reinstalled it and just rename the ab on the right side to for the above key to
Mozilla/4.0 (compatible; MSIE 8.0; Win32)
Both fixed the problem