Are you running Microsoft Virtual PC 2007 in Windows Vista?
Have you ever experience the stated error when running a VPC created using Microsoft Virtual PC 2004?
The virtual machine "<VPC Name>" can't be started because it is being used by another program, or marked as read-only. To start this virtual machine, stop using the virtual machine in another program, or ensure that it is not marked as read-only.
This is because of the application does not have the privilege to access the particular file.
Here is the solution:
1. Right click on your Microsoft Virtual PC shortcut from the programs.
2. Select on "Properties".
3. Select on the "Compatibility" tab.
4. Check on the "Privilege Level" to run the application as an Administrator.
5. Start the VPC and you're good to go!!!