DNS

One Domain. NT 4.0 Terminal server/Citrix metaframe 1.8. One DNS server just put in as the name server. While configuring, after establishing the primary zone and the reverse lookup zone, while I am adding hosts, some add in ok, others are tellingme that the reverse lookup zone can not be referenced. I can nslookup both ways on the ones that add ok, and only one way with the ones that do not. Why? Can I add the entries that do not establish the correct ptr record to the in-addr.arpa file manually?