When you try and expand public folders if you get the error message "Existing connection was forcefully closed by remote host Facility win32 ID:C0072746"
Users will not be able to access OWA anymore
To fix this:
You need to re-apply the Windows service pack you have on the box and that will resolve the issue also if you are running Windows Server 2003 Sp2 make sure you disabled the Tcp chimney going to the command promt and typing
C:\> Netsh int ip set chimney DISABLED