An member server has some application using service account to query active directory for users and groups. I am using LDP to connect/bind and do queries using LDP.exe , "Bind" works succesfully with the account, "LDAP Search" works with both LDAP and LDAPS;the issue is, they are doing something called "Virtual List View" query and its throwing up error when subtree is used; below are my questions.

Whats is the difference between SEARCH and VIRTUAL LIST VIEW?
 Why does VLW work when"one level" is selected and it throws out an error ("Unavailable Critical Extension") when "subtree" is selected?