The rotary spindle has jammed

Be sure the bobbin winding spindle is full to the left.

You may need to clean/oil the machine.

http://www.menwhosew.com/how-to-clean-and-oil-the-singer-heavy-duty-sewing-machines/

Hello Christine, I think you do have a thread stuck between the rotary hook and the bobbin case carrier. Remove the bobbin case and bobbin. You will need to remove two small slotted head screws and remove the half circle locking ring that holds the bobbin case carrier in place. Try to wiggle the bobbin case carrier one way and than the other until it comes out of the rotary hook assembly. Don't pry too hard or you might damage the carrier and/or rotary hook assembly. Once removed, I think you will find the thread that is causing the lock up situation . Before reassembling, place a drop of oil on the bearing surfaces between the carrier and rotary hook assembly and also between the locking ring and the carrier.

try to take the needle out of the needle holder & see if you can clear the
jam that way

normally when the spindle won't move it's possible that is damaged or a broken part
try some sewing machine oil on it & see if it will free up the spindle

try some sewing machine oil on it to see if it will free up the spindle

clean out rotary hook area following manual instructions on how to do this, usually removing bobbin holder and bobbin, then the rotary hook area by undoing the latches each side.

Could be a thread jamming in there causing the error message.

This image shows that you need to oil the needle bar bearings and the rotary hook area. Also, always brush clean the rotary hook area after each use as keeping lint ouf of moving metal parts will prolong the life of any sewing machine and let the oil do its job.

Also, use good quality clear sewing machine oil, just a drop in the points indicated.

Check the bobbin winder rubber, it may be worn or broken and insufficient friction against handwheel to turn.........or a thread jam around spindle is stopping the spin. In this case, carefully unwind, DO NOT cut thread.

The bobbinwinder spindle is on the top of the machine on the right.

Try to turn the spindle with your fingers. If it is turning easily, good. If not, see below.

Push the spindle to the right and it should turn when the handwheel turns.

If the spindle does not turn properly, remove the two screws that hold the top cover on. DO NOT REMOVE THE SCREW THAT IS ON THE SMALL BLOCK NEXT TO THE BOBBINWINDER SPINDLE.

The top cover will not remove because of the handle. While lifting up the cover, peer under to make sure that there is a small rubber tire on the under side of the bobbinwinder spindle.

If the tire is there, place a small drop of oil on the spindle and turn it until it frees up. Try not to get oil on the tire, it will make it slip. Wipe it off if it gets oily.

Replace the top and retry.

Sounds like you need to put a drop of clear sewing machine oil in the raceway of the hook. Then sew on some scrap material to soak up the excess oil.