Absolutely no need to apologize for your question – obviously it was not such an easy one if it took so long to receive some answer.
From what you described I can imagine just a three possible problems:
- If you enable NetBIOS resolution on Netflow Setting page, Netflow service is using only NetBIOS. But you also wrote that NTA seems to be able to resolve external IPs, so than this doesn’t seem to be your case.
- NTA service can send hundreds of request to your DNS server if resolution set to persistent, so this can stop respond if configured to prevent DNS flood attacks.
- There is some internal problem in NTA.
In a case that you will be able to refute first two cases, than I would definitely suggest you to submit support ticket, so that our stuff can closer investigate your problem.