This leads us to a great division in Christian doctrine, primarily between East and West. In West (Roman/Latin) Christianity, "sin" has been defined almost exclusively as "spiritual crime". That is, one must fulfill all the normal prerequisites of criminal liability to be "guilty" of sin. In Eastern Christianity, "sin" is defined in many ways, including with medical analogies. In addition, the original Greek and Hebrew words from Scripture are kept in mind, and neither of them translate as "crime" but instead translate more as "missing the mark". Thus, it is not unthinkable in Eastern Christianity to ask forgiveness for "sins both intentional and unintentional". The Roman/Latin Christian, having been brought up in a highly legalistic background, often is brought up short or even outraged by such a thought as an "unintentional sin", even though such is mentioned in Scripture (Luke 12:47-48, many mentions in the Old Testament). Of course, Christians are not expected to adhere to the multiple details of Mosaic Law (Acts 15), but the concept of unintentional sin was not exterminated, at least not early on. Later, when an obsession arose over legalistic reinterpretation, the idea of an unintentional sin became intolerable.
For those who might consider such a concept to be "unfair" to people who "try their best", consider Matthew 5:48. Christ does not say "do the best you can". It's an extremely high standard, but we are nowhere told that falling short of this standard is a guarantee of condemnation.
Therefore, "erroneous" is a form of "sinful", it's just not the Roman/Latin legalistic form of "sinful".
That being said, the term "deadly sin" is an innovation. The original work was in Greek, and they were known as "logismoi"--the "thoughts". Evagrius of Pontus singled out eight thoughts that he considered particularly dangerous, and he portrayed them as demonic tempters:
http://www.earlychurchtexts.com/public/evagrius_of_pontus_eight_logismoi.htm
It was response to the temptation that mattered, not merely being tempted.