When you try to save a Netmon.exe caputure file to a different folder than the default, you receive:
You cannot access '<Drive:>\<FolderName>'. This is because Network Monitor is running with reduced access in which administrator privileges have been removed.
To gain access, add your user name '<UserName>' to the permissions list of this file or folder.
NOTE: You receive this error even if you are logged on as a member of the local Administrators group.
This behavior occurs because Netmon.exe in Windows Server 2003 no longer runs with administrator credentials.
To workaround this behavior, grant your user account explicit permissions on the folder.