You may have a long LDAP filter for some of your PeopleSearch and PeopleUpdate queries. Generally, long filters work just fine but you may get errors like a Page Cannot Be Displayed message.
Internet Explorer 8 and older versions of IE have length limits on the URL and posted data so this might be part of the issue. You can try to make your query length shorter or break the query into a couple of different parts for different task items to help remedy the situation.
Check out http://support.microsoft.com/kb/208427 for more information about this limitation.