Me too, the computer was just resetting every 10 - 15mins, that's a pretty serious issue.
Reading the three updates I'd hazard a guess that
Microsoft Security Advisory (932596) is the culprit. It is possibly conflicting with Sandboxie. They've always said the x64 version was living on borrowed time.
Windows Vista 64
Sandboxie cannot be installed on Windows Vista, x64 Editions for the following two reasons.
Driver Signing
With Windows Vista x64, Microsoft has introduced mandatory code signing for drivers. Since Sandboxie relies on a driver component to ensure software isolation, it cannot be loaded into Windows Vista x64 without compromising the integrity of the system.
Acquiring the code signature is not in itself an insurmountable task. However, the next reason will show why this is pointless at this time.
Kernel Patch Protection (PatchGuard)
In 64-bit editions of the Windows platform, Microsoft has extended the core of the operating system, the kernel, in such a way that it routinely performs self-checks to detect any tampering. This miracle of an extension is affectionately nicknamed PatchGuard.
The software isolation provided by Sandboxie is not something that the stock Windows kernel supports, and in order to implement this, Sandboxie must make some changes to the kernel. This is detected by PatchGuard as tampering, and so the system crashes soon after Sandboxie is installed.
Note that the PatchGuard used in earlier versions of Windows x64, specifically Windows XP 64-bit Edition, is less aggressive than the PatchGuard used in Windows Vista x64. For this reason, Sandboxie can and does work in earlier editions of Windows x64. For now.
Maybe it's nothing to do with it, I am only guessing, I'll follow their forums and see if anything turns up.