It is often recommended to uninstall the previous version of Arnold to avoid "ghost" plugins in the C4D bridge.
Warning: Using Arnold 440 on R21 without a valid rental or perpetual license triggers a watermark. No "cracks" are stable for this version.
And somewhere, in a forgotten corner of the internet, the ghost of SolidAngle still waits, ready to turn light into truth for anyone desperate enough to believe.