Child Active Directory Authentication

I’ve just installed Openfire 3.6.4 and am using LDAP authentication on our Windows 2003 parent domain which works great. However, we have users in a child domain which cannot authenticate. LDAP is pointed to the root of our parent domain as is using the administrator account for ldap queries. So, authentication to parent.local is fine, but branch.parent.local does not authenticate.

Any ideas?

Update- Since we have way more than the 1000 user limit, I’ve implemented a search filter to only use members of a security group in the parent domain. I made this an Enterprise security group and added a user from the child domain, but still no luck. The user from the child domain also does not show up in the users/group page.