This one is rather straight forward.
- Get the domain controller for the given domain name
- Invoke Knowledge Consistency Checker (kcc)
- Enumerate all other domain controllers that are known to the domain controller for errors
- Report the total error count to PRTG
See also http://msdn.microsoft.com/en-us/library/system.directoryservices.activedirectory.domaincontroller.checkreplicationconsistency(v=vs.90).aspx
please try to run the ADSReplFailures.exe from command line to check which DC reports the errors.
file should be in the PRTG Program folder
e.g. C:\Program Files\PRTG Network Monitor\Sensor System