i try to configure forwarding to another DNS.

What i have done:

I have setup a DNS-Server (OES2SP2) which manage a subdomain
(lab.mydomain.tld) this server is the primary. The zone lab.mydomain.tld is
the only zone (but there is an reverse lookup zone).

This server runs fine, no problem.

In the local Main-DNS server (OES2SP2) (designated for mydomain.tld) i have
created an forwarding zone. Name: lab.mydomain.tld the designated server is
the Main-DNS serer, too. In the forwarding list of the zone i have added the
IP of the DNS in the subdomain.

You may to know, that both DNS-Server are in different Trees.

But if i try to resolve examplehost.lab.mydomain.tld the Main-DNS can't find
it. If i ask the subdomain-DNS the resolving is correct.

What is my failure?
Any hints?

Is forwarding the wrong way? Have i to use Primay/Secondary zones?