A coworker ran into a problem the other day that I wanted to highlight for those who may run into this.  First off, never, ever resize a VHD that has snapshots on it.  Snapshots are child objects that relate to a VHD and they map changes to certain places in the VHD.  When you resize a parent VHD, the child VHDs have incorrect references and this needs to be corrected.

You can fix the problem with VHDtool.exe.  The program is a bit hard to find now but once you find it, the process is quite straightforward.