Just to be sure we're all on the same page - LightMix never worked with .exr files, only with .cxr files (which are Corona's modification to the exr file format, containing extra custom data needed for denoising and lightmix). So, do you mean you have a .cxr file that used to load with LightMix but now it doesn't? Or do you mean you accidentally saved from Corona to EXR (in which case, LughtMix would not be expected to work)? Or you are saving to a CXR file as needed, but LightMix isn't working in the CIE after that?