Syntax error: unexpected token < in JSON at position 0

I have a problem with user registration and delivery method and payment method.
I've installed a fresh copy of opencart 2.1.0.2 and still have the same problem.
If I input something in the fields (non required ones) there is no error, but if not, I get the errors in the picture.

I've searched the forum for this error, but I found only that I have to modify the customer.php; shipping_method.php and remove the fields that gave the errors.
I did that so the user can register, but now the fields in the database are not recorded, they are empty.

Can you help me resolve this issue?

Patches can be found here: http://forum.opencart.com/viewtopic.php ... 66#p617203 and here: http://forum.opencart.com/viewtopic.php ... 66#p618051

Thank You, you saved me. I've searched a lot of posts, but it seems I was blind

Hello, a have a problem like this, any help