Slackware 13.1 no longer boots (kinda)

[electronpusher_det]

I have a Virtualbox host(Version 4.0.4 r70112)running on a Windows 7 64-bit Enterprise host(patched to the most current level, as of 4/3/2011). It has a Slackware 13.1 64-bit guest, which was running normally. I was tinkering with X, trying to get it to run on the guest. I ran the xorgsetup, accepting any defaults. I then ran startx, whcih locked the guest's virtual console. It was unresponsive to any input, including keyboard, mouse or sending either an ACPI shutdown or a control-alt-delete from the guest console window. I killed the guest by using the "Machine menu->close->power off the machine" sequence. The next time I tried to boot ther guest, it failed, with this error: "A critical error has occurred while running the virtual machine and the machine execution has been stopped." I have been able to boot the guest by using the guest OS installation DVD, and from there to execute a graceful shutdown, both OS initiated, and initiated from the guest machine menu, but it still will not boot fom the virtual disk. I also tried exporting the guest and importing it again, and it still had the same error when attempting to boot. The guest had the guest additions installed before the X setup, but they wouldn't load after the system crash. I reinstalled them after booting from the installation media, but this had no effect as far as I could tell.

Anyone seen this issue before, particularly with Slackware? More to the point, how can I recover it? I've got a fair amount of work invested in this image that i would have to repeat, if I can't recover it. I've spent several days building this image up, and I'd planned to take a snapshot after getting the X running, but I guess I crapped out on that one.