I'm pretty sure it means that the shader is missing. NULL. Is that part of Reshade? If so, try downloading again.
Settings fine for every other scenario - this is one on the GA Somerset and Dorset so assume must be to do with some item in the 3 linked scenarios. I run TSC in Borderless with no issues. Not sure If I even have Reshade installed. Will probably just dump those 3 scenarios thanks all. Resolution is 3440 x 1440 FXAA +4 x MSAA which works fine on other scenarios.
Thanks guys - as only 3 linked scenarios I will delete as everything else ok. Just wish error messages were more helpful.