I know there are some topics about this error but in my case it's different.
SuperSU has always been working until now, I flashed it on my OnePlus One from the beginning on with TWRP.
But now it suddenly stopped working, I don't know why. I didn't update anything I just tried to activate ART that day, rebooted, but it didn't apply, so I just stopped trying. But it can be that it stopped working before, I dont know when exactly..
I already tried:
Reflashing it over TWRP (No errors reported, just seems to install fine but still not working)
Wiping Cache and Dalvik (It's regenerated at start so Dalvik seems to work fine)
I checked it with Root Checker, it says that the are no binaries installed.
OnePlus One 64GB Sandstone Black
Cyanogenmod 11S XNPH33R