issue with Windows Domain Agent

issue with Windows Domain Agent

Hi, I  have:
1. Win server 2012 - Primary PMP
2. Win server MSSQL DB - Primary DB
3.  Win server 2012 - Secondary PMP
4.   Win server MSSQL DB - Secondary DB
PMP version 7.5
Wen I try to install Windows Domain Agent  I get the issue "Certification verification failed".
Can you help please. 

Domain Controller - Win Server 2008 R2.
                New to ADManager Plus?

                  New to ADSelfService Plus?