The rear calipers needs to be twisted in order to have the piston in. The X shape is to twist it with a tool all the way in.

Make sure you twist it clockwise all the way. There is a procedure for the emergency brake cable adjustment.

It goes something like this:
Make sure you pump the brake to pressurize them.
Lift the two rear wheels, then pull the e-brake two clicks. adjust the cable so the wheels start to drag. They should be loos when the e-brake is down all the way.

If you can't do it, it indicates that the caliper piston is not touching the rotor. I would go and twist the piston back in again. If it simply doesn't work, then it could indicate a problem with the caliper or cable.