HI Thanks everyone for prompt reply. Here are details. I work in an organization where I shutdown my all servers in the evening. We are using exchange 2003 and windows2000 Advance server. In the morning when I started my exchange server machine, its LAN card was uninstalled, I tried a lot to install but unable to install (it happens usually when your machine is infected by virus) so I tried to use Norton antivirus for virus scanning but antivirus was unable to start scanning .finally I fixed this hard drive to another system as a slave drive and scanned for virus, After scanning, I put this hard drive back in to exchange server. Now I was able to install LAN card. After installing LAN card, exchange mailbox store was un mounted. When I tried to mount mailbox store I received this message (An internal processing error Has occurred. try restarting the Exchange system Manager or the Microsoft Exchange Information store service, or both. ID no: c1041724 Exchange system Manager) Event viewer application error is (The MAPI call ?OpenMsgStore? failed with the following errorThe Microsoft Exchange Server computer is not available.Either there are Network Problems or the Microsoft Exchange Server computer is down for maintenance.The MAPI provider failed Microsoft Exchange Server Information store ID no: 8004011d-0526-00000000) I think now I have provided all information. Regards, shahir --------------------------------- Yahoo! for Good - Make a difference this year.