Thanks again everyone.
After a removing most traces of Guru on my system, down to the registry, several re-starts and finally followed by a new install I now have a working (fresh) version of GURU.
@smallg - now that you mention it the offending item could be the map I was working on. I did not consider it earlier because the last thing I did before saving was run the level - which ran flawlessly including all the scripts and then I saved before closing Guru normally.
When chasing my own tail I did a win file system verification using the sfc/scannow on command prompt and windows came up clean. To my logic this said that the Win 10 core system files were ok at any rate.
Also, support got back to me quickly (thanks Daniel) and suggested I download the latest DirectX End-User Runtimes (June 2010). I have not done this as my problem seems to be resolved but it is good information to have none the less.
Now to re-load everything back into guru.
Thank you everyone for the help. Amazing community.