VirtualBox problem in F15

[Patrick O'Callaghan]

I reinstalled VB in my (fully updated) F15, using the x86_66 RPM from 
the VB Downloads page. However when trying to start a saved Windows VM, 
I get this:

Failed to open a session for the virtual machine Win7.
pdmblkcache#0: The VM is missing a block device. Please make sure the 
source and target VMs have compatible storage configurations [ver=1 
pass=final] (VERR_SSM_LOAD_CONFIG_MISMATCH).

Result Code:
NS_ERROR_FAILURE (0x80004005)
Component:
Console
Interface:
IConsole {515e8e8d-f932-4d8e-9f32-79a52aead882}

I haven't touched my home directory where the VM is kept, so any light 
on this would be welcome.

poc