Event logged in the DNS Server log when a query is received for a name that exists in an authoritative zone, but is also on the global query block list:
EventID : 7600
MachineName : lab-dc1.lab.net
EntryType : Warning
Message : The global query block list is a feature that prevents attacks on your network by blocking DNS queries for specific host names. This feature has caused the DNS server to fail a query with error code NAME ERROR for wpad.lab.net. even though data for this DNS name exists in the DNS database. Other queries in all locally authoritative zones for other names that begin with labels in the block list will also fail, but no event will be logged when further queries are blocked until the DNS server service on this computer is restarted. See product documentation for information about this feature and instructions on how to configure it.
Below is the current global query block list (this list may be truncated in this event if it is too long):
wpad
isatap
Source : DNS
Resources:
http://divinal.wordpress.com/2011/08/27/event-id-7600-and-wpad/
Good explanation