The problem is in Reverse Lookup Zone. See there. I'm sure there is no records about your host.

Or may be Reverse Lookup Zone was not created at all (if so - create it!
To resolve the problem, go to Forward Lookup Zone, find "A" records (for example: NAME_OF_THE_DC - Host - IP Address), remove it, right click, choose "New Host...", type the same name and IP addres And check "CREATE ASSOCIATED POINTER (PTR) RECORD"
Go to Reverse Lookup Zone. Refresh it. There will be the record (IP addres to Hostname). If the record exists than NSLOOKUP will work properly
Best regards
Igor Fomin, igorf ==at== digdes == co