The error message in the syslogs is:
Unable to resolve ICAP XAUTH URI "WinNT://domain/User" using LDAP
Network Prevent for Web or Network Prevent for Web Virtual Appliance
In the past we have seen these issues due to the base DN being too specific.
Change your base DN to a higher, more inclusive level, e.g.,
"DC=example,DC=com"
(replacing example and net with the correct values)
Incidents should now be reported with usernames.