I am having the same issue, I only have MM 3.0.4 installed. It seems to be random, but always after the patches are finished. If I remove realism overhaul through ckan, which also removes real fuels, and real plume, then everything loads fine, albeit somewhat unusable with half an RP1 install. I have tried different versions straight from github, no success. I have taken everything from the golden spreadsheet for 1.3.1 ....also clean install of 1.3.1 straight from steam. I have had issues before i could work out, but this one has me stumped.