Cannot boot after vhd hard drive is resized in VirtualBox

Unfortunately the VirtualBox documentation for the VBoxManage --resize option is misleading. You cannot just increase the size of the disk image and have everything work properly. The disk partition information within the image has to be adjusted so that the guest operating system knows the layout of the "drive" the disk image is simulating. You accomplish this adjustment by downloading a bootable CD image that has a partition editor on it and booting the VM onto that CD. You then use the partition editor to adjust the disk image's partitions to use the added space.

There's a nice writeup of the procedure here; just skip to step 4.

I had the same issue

1. create new VHD with desired size
2. Use clonhd to copy from old vhd to new vhd

Reference : http://tips.kaali.co.uk/2012/03/16/expand-or-increase-the-size-of-virtual-box-vdi-dis/