VBox Manager crashes when taking snapshot

[larrry]

I'm running Windows 7 HP 64, VirtualBox 4.0.0 with several Linux guests, two of those Debian Linux.
In one I'm running Debian 2.6.33 - not sure whether this is relevant, which is why I mention it.
After some copying of data to/from a USB stick, I took a snapshot to save my work. In the middle of this process the message appeared 'Oracle VM VirtualBox Manager funktioniert nicht mehr (stopped working)'.
Prior to this happening I installed the Oracle_VM_VirtualBox_Extension_Pack-4.0.0-69151 hoping that this would fix the problem of the USB stick being released after I shutdown one of those Linux VMs. What happened was, that the USB stick was no longer visible to Windows; removing and re-plugging did not fix this, only rebooting of Win7.
However, now the VM I tried to save by way of a snapshot, no longer starts. I tried to remove the USB filter, but it still won't boot.
Re-imported the original state from an OVA and made the amendments as before i.e. copy & move files.
Shutdown Linux using shutdown command, Linux reports 'system halted', but the VM window does not close. Have to use 'Host + Q'.
Took snapshot of VM and then tried to start it. It crashes again during boot.

[larrry]

Updating VirtualBox to 4.0.2 fixed the problem.