For the SMC Agent to connect to the SMC Server, the following requirements must be met:

SMC Server needs access to the client's hidden share C$ (\\<client_IP_address\c$\).
It is also important, how you access this share. If you are not asked for user data, then you need to be domain administrator, to carry out the installation.
In this case, type Domain\Administrator as username, and the administrator's password, during installation.

The Guest account has to be deactivated.
Simple file sharing must also be inactive: Explorer → Tools → Folder Options → View → Use simple file sharing (Recommended).

Firewall - If you use a firewall, enable the following ports (TCP):
Out (TCP): 7000, 7001, 7010, 7020, 7021, 7030, 7050, 7051, 7080, 7100.
In (TCP): 7030
You also need to allow ICMP requests and PING (incoming echo requests).

Alternatively, you can install SMC Agents manually, by running the installation file, or unattended, using a script.

The following folder has been created on SMC Server:
C:\Documents and Settings\All Users\Application Data\Avira\Avira Security Management Center Server\Agent\.

Share this folder with write permission, if not shared already during the installation of SMC.
For the unattended installation, you only need to run the file installagent.bat over the share:
\\<SMC_server_IP_address>\<share(Agent)>\installagent.bat

The script installagent.bat calls the installation routine setup.exe of the SMC Agent and uses the information from the file installsmcagent.iss
If an uninstall batch file (for example, uninstallagent.bat) is created, for uninstalling the SMC Agent, it can use the file uninstallsmcagent.iss.

The clients on which SMC Agent was installed unattended, will be added in a new node of the Security Environment, called New Computers.
You can move them by drag&drop, as you wish.