Is it also Paul's error?
Romans 7:18 For I know that in me (that is, in my flesh,) dwelleth no good thing: for to will is present with me; but how to perform that which is good I find not.
19 For the good that I would I do not: but the evil which I would not, that I do.
20 Now if I do that I would not, it is no more I that do it, but sin that dwelleth in me.
21 I find then a law, that, when I would do good, evil is present with me.
22 For I delight in the law of God after the inward man:
23 But I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members.
24 O wretched man that I am! who shall deliver me from the body of this death?
25 I thank God through Jesus Christ our Lord. So then with the mind I myself serve the law of God; but with the flesh the law of sin.
You responded: Is it also Paul's error?
No, it is merely Luther presuming that man's nature is totally destroyed as a result of Adam's sin. Paul correctly realizes that man is wounded, that we, the flesh, cannot forever avoid sinning. It is only grace-aided man who is able to be consistently righteous in God's eyes, as Paul goes on to relate. Paul doesn't simultaneously call man saved and a lump of manure...!
The sum of Luther's error can be traced to his conception of man before and after the fall of Adam.
Regards