Hello, I have two Exchange server 2003 clusters. After installing Win 2k3 SP1 in them both of them became inaccessible. No one can access his mail box. Server themselves showed lot of error. I was unable to open Cluster Administrator window and lot more errors in event logs. After uninstalling Win 2K3 SP1 every thing became normal. Now both Exchange clusters are in live with about 250 mailboxes in each. Currently I am facing a problem related to RPC error that restarts servers those do not have SP1 installed. I think installing SP1 in those servers (Exchange Clusters) will solve the problem. I need to know if there is any special procedure to install the Win server 2k3 SP1 in exchange clusters. Do I require any Patches or Hot-fixes? Please reply. Thanks lot for your earliest attention. Best Regards, Osman Mahmud