virtualbox.org

I have a very similar issue. Win7 X64 host system. Win XP 32 guest. No issues on 4.2.16. After upgrade to v4.2.18 If I add a USB stick to the guest OS and unplug it before doing a 'Safely remove hardware' XP throws an error. If I then try and take a snapshot VBox throws an error and I have to roll back the VM.
Also ignoring the USB issue, I can only take one snapshot with 4.2.18. If I try to take a second snapshot VBox errors as above. However if I shutdown and restore the first snapshot I can then take a second. So as long I stop and re-start the VM between snapshots I'm ok. As for the USB, as long as I do a safe removal prior to taking a snapshot I'm ok.

If I take a snapshot with a USB stick attached, when I try and restart the snapshot it fails saying theres a piece of hardware missing from the VM.

I need to roll back to 4.2.16.

I just installed 4.3.0 and the issue appears to be resolved in that release. However, I also re-imaged windows 8 and upgraded to 8.1 in the mean time. So, anyway it appears 4.3 solves the problem for me.