Can't create any VMs on Windows 8

[StarNamer]

I recently installed VirtualBox 4.2.6 r82870 on Windows 8, but every time I try to create a VM I get an error:

Code: Select all

Failed to open a session for the virtual machine Mint 2.

Failed to assign the machine to the session (Unknown Status 0x80004005).

Result Code: VBOX_E_VM_ERROR (0x80BB0003)
Component: Machine
Interface: IMachine {22781af3-1c96-4126-9edf-67a020e0e858}
Callee RC: E_FAIL (0x80004005)

The CPU is s T5750 (64-bit, but no VT-X support) but it's not getting as far as installing the OS so it's not a 32/64 bit problem or related to another VM running.

What do I do to fix this?