I would check the following Items first:
1. Make sure that you do not already have an Identity Source already setup for Active Directory (I did this and fell stupid about it)
2. Make sure the ID you are using has rights to join the domain where you are trying to place the vCenter or (for external Platform) the Platform server.
Example of me adding my vCenter to our AD
you need to have full rights on this OU
Name: my\administrator or email@example.com
This user needs to be a domain user
I hope this helps. If the Administrator is a domain admin account it should work without an OU, but I personally would put my computer objects in a new OU instead of where AD puts all of the pre-configured computer objects
Please login with root user and make sure the user which you are using have privilege to add the user.
- Allow TCP 445 from the VCenter appliance to the Domain Controller.
- The Qualified Username not the Windows format.
Command PowerCLI for insert in the doman.
/opt/likewise/bin/domainjoin-cli join <your domain> <user name>