The toolchain is unable to build a dummy C file when building project with toolchain manager install

I've been trying to build blinky using the nRF SDK from the toolchain manager with no success on windows 10. I've previously been able to build projects so I'm not entirely sure what is causing this issue.  

I'm using the nRF connect VSCode extensions, the behavior is the same with Segger embedded studio.


Things I've tried:

- Clearing the cache (ncs\SDK_VERSION\zephyr\.cache)
- Fresh install of both nRF connect & SDK/toolchain (Uninstall connect, delete ncs, .nrf-connectapps & appdata, reinstalling VSCode extensions)
- SDK versions 1.7.0, 1.7.1 & 1.6.0
- Using an older version of CMake (3.17)
- Deleting build folder & using pristine build w/ VSCode 
- Error is the same with or without nRF connect command line tools

On trying to compile the blinky example (zephyr\samples\basic\blinky) to the board  actinius_icarus_ns (i've tried others e.g thingy:91 -- no success) the following error is thrown: 

CMake Error at c:\Users\USERNAME\Documents\ncs\v1.6.0\zephyr\samples\cmake\extensions.cmake:1746 (message):
  Assertion failed: The toolchain is unable to build a dummy C file.  See
  CMakeError.log.
Call Stack (most recent call first):
  c:\Users\USERNAME\Documents\ncs\v1.6.0\zephyr\samples\CMakeLists.txt:42 (assert)

Just wondering if maybe someone has experienced a similar issue? There is old threads with the same error but it seems to be a solved issue & none of the fixes are working (at least for me)


Thanks