How to lock file for moving VM?

I'm moving my virtual machine from drive "C" to "D" and I kept getting this error when trying to start the virtual machine.

Cannot open the disk ‘d:\virtual machines\mycomp\windows XP Professional-0000002.mvdk’ or one of the snapshot disks it depends on. Reason: Failed to lock the file.

Any help is appreciated.

By the way, I'm using the free version of VMWare Server.