If you are using Windows Vista, and you set the properties on the virtual machine to save and automatically restart when the host machine reboots, simply using an administrator account is not sufficient. It is necessary to turn off the user account control security in order to start the guest operating system.
This error occurs if the user account that is configured to run the virtual machine does not have access to the .VNC file describing the network. This file (one per network connection) is usually found in C:\Documents and Settings\All Users\Documents\Shared Virtual Networks. Grant the virtual machine service account access to the .VNC file - minimum permissions are:
* Execute File
* Read Data
* Read Attributes
* Read Permissions
Also see the link to "Modifying general virtual machine properties".