I also have the 'Unable to Read Scenario' error when trying to play Firestorm offline and trying to start a new campaign - either GDI or NOD. I am running via TSLauncher (TSPatch applied). I have no problems with Tiberium Sun - only with Firestorm. Firestorm loads fine - it just won't start the campaign - so I guess this is somehow related to ini/mix files mapping/settings etc. I can see the issue across many forums and many years - but cannot see the solution readily. Would love to get to the bottom of this - happy to provide and files, screenshots etc if that would assist.