Hi thanks for the quick response, I've just done a clean install of Steam and Factorio, unfortunately I'm still getting the same error.

Each time I load up Factorio, I get the same message on the main menu:
'Steam Error - Couldn't initialise Steam API. Steam related features are disabled. Restarting Steam usually fixes the issue. '

This is a problem I was also having before [16.36], when trying to change to from [15.40] to any of ...