We (ATFclan.eu) also get these DNS errors sometimes...
We tried to change our DNS server but without any results. :\
I also would like to know whats causing these errors, seems to be a blockland bug.
This is the error:
No user/host entry in master server, re-sending authentication request
Authentication: Sending Initial Request...
Authentication FAILED: DNS error.
sometimes even this:
ERROR: - Authentication DNS Failed. Retry 1
BackTrace: ->servAuthTCPobj::onDNSFailed