VBoxSVC crashes randomly on Solaris host

[sunflower]

At random intervals (sometimes a few hours, sometimes days) VBoxSVC crashes, causing all VMS running on the host to PowerOff. We are running Windows 7 and Windows XP guests on the same server. Definition for all VM's is identical. On average 25 VM's running on host, with plenty of resources available. All VM's show exactly same error in the logs.

Extract from one of the VM logs
===============================
06:19:59.358 Guest Additions capability report: (0x5) seamless: yes, hostWindowMapping: no, graphics: yes
06:20:02.391 RTC: period=0x20 (32) 1024 Hz
06:35:36.811 RTC: period=0x200 (512) 64 Hz
10:35:45.318 VirtualBoxClient: detected unresponsive VBoxSVC (rc=NS_ERROR_CALL_FAILED)
10:35:45.318 VBoxHeadless: VBoxSVC became unavailable, exiting.
10:35:45.319 Console::powerDown(): A request to power off the VM has been issued (mMachineState=Running, InUninit=1)
10:35:45.319 VRDP: TCP server closed.
10:35:45.319 Changing the VM state from 'RUNNING' to 'POWERING_OFF'.
10:35:45.319 ERROR [COM]: aRC=E_ACCESSDENIED (0x80070005) aIID={1968b7d3-e3bf-4ceb-99e0-cb7c913317bb} aComponent={Console} aText={The object is not
 ready}, preserve=false
10:35:45.319 ****************** Guest state at power off ******************
10:35:45.319 Guest CPUM (VCPU 0) state:
10:35:45.319 eax=0e9c4fbe ebx=ffdffc70 ecx=ffdffc70 edx=00005c82 esi=ffdffc50 edi=867c4948
10:35:45.319 eip=f1649162 esp=80551434 ebp=80551450 iopl=0         nv up ei pl zr na po nc
10:35:45.319 cs={0008 base=0000000000000000 limit=ffffffff flags=0000c09b} dr0=00000000 dr1=00000000