Not available: Failure occurred attempting to check the schema state

Hello everyone,
Around a month ago I have installed OCS 2007 R2 on my server named OCS (Windows 2008 R2 server) without any trouble. Now, when I try to install the Archiving server on it, it asks me to prepare my Schema and the installation is failing. I am getting the error given below.
"Not available: Failure occurred attempting to check the schema state. Please ensure Active Directory is reachable."
I made some modifications to my Ad and DC. I think this error is a result of it. Modifications I have done are as follows.
I have 2 DC
Alpha (Windows 2003 SP2 R2 server) as Primary DC
Beta (Windows 2008 R2 server)
DNS have installed on both of them and acts as Global Catalog.
Need some help for this?
Thanks.
