Radio error code e20

E20 is an error that means the laser that reads the information from the CD is not aiming properly and cannot focus. There are a few items that could cause it, a dust bunny on the lens being a common one, the next is a failure in the wires that power the read head.
You could try a cleaner CD, it is a CD with tint brushes on the surface that generate a breeze as the CD spins and can blow the dirt/dust off the lens. The other option would be to remove the unit and replace the CD drive in it or try using compressed air to clear the lens. None of these will change things if the problem with the physical read head however.
Just google for a CD/DVD lens cleaner to see what they are and where you can get one.