Monitoring your AD is something that needs to be done regularly, and there are many commercial utilities out there that will help you achieve this. However, it might be worth investigating tools that are available for free from Microsoft, and even from some other vendors.
Sonar and Ultrasound are two utilities that allow you to monitor the File Replication Service (FRS), and both utilities are good at detecting problems beforehand, or issues with replication from certain DCs. Sonar can be downloaded from the Microsoft Download Center at http://www.microsoft.com/downloads.
You will need to have the .Net Framework 1.1 installed on the machine where Sonar will run. Also, please be aware that if you have .Net Framework 2.0 installed, it does not include 1.1, and you need to install 1.1 as well.
Once installed, Sonar will not create a program menu entry, so you will need to search for it. For some reason, it will install itself into the Resource...