I always get the error message when installing the IPCC 4.0(4). The error message said that ".....unable to resolve dn because an ou was missing".
I checked my AD, and found the installation program created some OU on the AD tree.
Can someone hit this problem before?
It looks like an issue with the "Chase Referral" option when doing an LDAP search against Active Directory with a child domain.
ultimate fix was to point the IPCC install at the child DC, not the root DC. The Callmanager plugin apparently was able to follow referrals successfully.