problem with DNS in adding new DC

I have upgrade NT to 2k .after I have upgrade PDC
It asked me to install DNS .As I have read in ms docs
I leted it install DNS and It asked me for creat new zone.
I gave the NT domain zone name and got an error after
some minutes .It said couldnt creat the zone becouse the
zone is already exist .then it said It has installed DNS
anyway .
THe problem is :
the users could see the DNS and use it but when I try to
add another DC in to this mix mode domain it said it
couldent attached to DNS but it could see the domain.com.
I tried to connect it by BDCs but they could not see it either .
I removed and installed DNS again and creat new zone, (same name)
but again I couldn`t see it during dcpromo process .
any idea ?
will it makes problem during other bdc`s upgrade ? is it
becouse it is in mix mode ?