This paper presents a new version of Robo-Sensei's NLP (Natural Language Processing) system which updates the version currently available as the software package "ROBO-SENSEI: Personal Japanese Tutor" (Nagata, 2004). Robo-Sensei's NLP system includes a lexicon, a morphological generator, a word segmentor, a morphological parser, a syntactic parser, an error detector, and a feedback generator. The present paper focuses on the error detector and the feedback generator and describes how those components are integrated into Robo-Sensei's NLP system, what types of errors are detected, and what kinds of feedback messages are generated. The author is currently developing a new Robo-Sensei online textbook (Nagata, in press). The updated system is the NLP processing engine behind the new textbook. (Contains 2 figures and 8 notes.)