The best method to determine the appropriate setting for the AD Group Distinguished Name field can be found by using the Sysinternals AD Explorer tool, which is available on the Microsoft Technet website.
After you have downloaded and installed AD Explorer:

• Establish a connection with the AD server using AD Explorer.
• From the AD Explorer interface, browse and select the group that you are trying to synchronize with.
• Once the correct group is selected you will be able to see the path near the top of the AD Explorer window (copy and paste this path into the Uptime Infrastructure Monitor field).

The result should look similar to:

OU=Employees,DC=domain,DC=com,dchost [dchost.domain.com]

In this example, the AD Group Distinguished Name would be:

OU=Employees,DC=domain,DC=com