My site requires CSS optimization to work with IE because of the number of css files from contributed modules. This is usually no problem, but I've come into work today and CSS optimization is off and the option to turn it on in /admin/settings/performance is greyed out. I've tried searching but can't find any similar experiences. Anyone? I'm looking into restoring from backup, but even if it works, it might happen again so it would be good to see if anyone knows what might be going on.