Logging into the Windows 2003 SBS Server virtual machine, I got that it unexpectedly shutdown. Event Log:
Event Type: Error
Event Source: System Error
Event Category: (102)
Event ID: 1003
Time: 3:13:29 AM
Error code 00000077, parameter1 c0000185, parameter2 c0000185, parameter3 00000000, parameter4 03278000.
Looked thru logs (filtered it so I would only see eventlog events) to find when it restarted. Found it restarted when I was doing some testing scripts of suspending other VMs and running rsync to back them up. So lots of disk IO.
Found others have seen this and applied the following
In the registry, go to HKEY_LOCAL_MACHINE/System/CurrentControlSet/Services/Disk.
Click Edit/Add value.
Set the value name to TimeOutValue.
Set the data type to REG_DWORD.
Set the data to 0x03c hex
Reboot the virtual machine.
So I did this.