How to recreate re-create the Outlook Web Access-related virtual directories

Step 1: Delete and then re-create the Outlook Web Access-related virtual directories

To delete the Outlook Web Access-related virtual directories, follow these steps:
Start the Exchange Management Shell.

Type the following commands. Press ENTER after you type each command.

Note: These commands are case-sensitive.

Remove-OwaVirtualDirectory "exchange (default web site)"
Remove-OwaVirtualDirectory "public (default web site)"
Remove-OwaVirtualDirectory "exchweb (default web site)"
Remove-OwaVirtualDirectory "owa (default web site)"

To re-create the Outlook Web Access-related virtual directories, type the following commands at the Exchange Management Shell.

Press ENTER after you type each command:

New-OwaVirtualDirectory "exchange" -OwaVersion Exchange2003or2000 -VirtualDirectoryType Mailboxes -WebSiteName "Default Web Site"

New-OwaVirtualDirectory "public" -OwaVersion Exchange2003or2000 -VirtualDirectoryType PublicFolders -WebSiteName "Default Web Site"

New-OwaVirtualDirectory "exchweb" -OwaVersion Exchange2003or2000 -VirtualDirectoryType Exchweb -WebSiteName "Default Web Site"

New-OwaVirtualDirectory -name "owa" -OwaVersion Exchange2007 -WebSiteName "Default Web Site"

http://support.microsoft.com/kb/941201