If you have a multi-subnet network with Active Directory deployed as a single domain with multiple domain controllers, and you find that users on one subnet can no longer see network resources on other subnets, it may be that your domain controller that has the PDC Emulator role is offline. This is because the PDC Emulator always hosts the Domain Master Browser role for NetBIOS browsing using the Browser Service, and if this role is missing then domain controllers on other subnets (which act as Master Browsers for their subnet) will be unable to update their browse lists.
Mitch Tulloch is President of MTIT Enterprises, an IT content development company based in Winnipeg, Canada. Prior to starting his own company in 1998, Mitch worked as a Microsoft Certified Trainer (MCT) for Productivity Point International. Mitch is a widely recognized expert on Windows administration, networking and security and has written 14 books and over a hundred articles on various topics. He has been repeatedly awarded Most Valuable Professional (MVP) status by Microsoft for his outstanding contributions in supporting users who deploy Microsoft platforms, products and solutions. Mitch is also a professor at Jones International University (JIU) where he teaches graduate-level courses in Information Security Management (ISM) for their Masters of Business Administration (MBA) program. For more information see http://www.mtit.com.