I exported a OBJ from 3dmax in a CM scale, object has 50cm, when i import it into zbrush the object is so large that even brush with draw size 1000 which is the highest possible numer is too small to sculpt on my imported OBJ.
I guess you didn’t GoZ from Max. If you go to the deformation panel and hit ‘unify’, you should be able to sculpt. If you have to export back out, I’m not sure of the outcome, maybe GoZ will maintain your scale?