I don't want to sounds like a broken record but, if the error message your getting says 'non zero rotations' then your bones have rotations, and thats the root cause of the problem. on the note, if I do recall correctly (and it's been a long time, so I could be wrong), sometimes bones may have a -0 rotation or even a 0…
You can change the scale of all the joints in the scene with Display > Animation > Joints Size. Or you can change the Radius attribute of a single joint to resize it individually. Non-zero rotations is just what it sounds like. You have been rotating your joints and therefor Maya can't orient them for you. A quick way to…
I usually make one trashCopy of my skeleton first where I go nuts with translating and rotating joints. Add it to a new layer and set it to reference. Then I create a new joint system where I just snap the joints to the old joints positions.