Validate system requirements when starting VM

I'm running FreeNAS virtualised on ESXi 6.7. I've tried a number of times to start a Rancher VM by following the setup instructions, but every time i try to start the VM, i get this error

Request Method: POST
Request URL: http://192.168.1.220/legacy/vm/start/12/
Software Version: FreeNAS-11.2-BETA2 (f14b2ed0e)
Exception Type: ClientException
Exception Value:
[EFAULT] VM RancherUI failed to start: vm_create: Device not configured
Exception Location: /usr/local/lib/python3.6/site-packages/middlewared/client/client.py in call, line 437
Server time: Sat, 25 Aug 2018 09:59:39 +0100

Environment:

Software Version: FreeNAS-11.2-BETA2 (f14b2ed0e)
Request Method: POST
Request URL: http://192.168.1.220/legacy/vm/start/12/

Traceback:
File "/usr/local/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
42. response = get_response(request)
File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py" in _legacy_get_response
249. response = self._get_response(request)
File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
178. response = middleware_method(request, callback, callback_args, callback_kwargs)
File "./freenasUI/freeadmin/middleware.py" in process_view
163. return login_required(view_func)(request, *view_args, **view_kwargs)
File "/usr/local/lib/python3.6/site-packages/django/contrib/auth/decorators.py" in _wrapped_view
23. return view_func(request, *args, **kwargs)
File "./freenasUI/vm/views.py" in start
86. c.call('vm.start', id)
File "./freenasUI/vm/views.py" in start
86. c.call('vm.start', id)
File "/usr/local/lib/python3.6/site-packages/middlewared/client/client.py" in call
437. raise ClientException(c.error, c.errno, c.trace, c.extra)

Exception Type: ClientException at /legacy/vm/start/12/
Exception Value: [EFAULT] VM RancherUI failed to start: vm_create: Device not configured

Request information
GET
No GET data

POST
Variable Value
__form_id 'form_str'
FILES
No FILES data

COOKIES
Variable Value
fntreeSaveStateCookie 'root%2Croot%2F11%2Croot%2F70%2Croot%2F70%2F77%2Croot%2F70%2F72%2Croot%2F9'
csrftoken '********'
sessionid 'zue9ymdkym2dw20jfc2jwqengd7j24w5'
META
Variable Value