Although chat-based reference services have been studied for over a decade and guidelines have been developed for effective communication in virtual reference service, little is known about the actual sources of miscommunication in these interactions. Our study uses a conversation analytic framework to investigate the types of potential or actual problems in communication that occur between librarians and patrons in chat reference interactions at a university library. Conversation analysis methodology, as developed by Harvey Sacks, Emanuel Schegloff, and Gain Jefferson, provides an empirical basis for claims about problems with communication by investigating what the participants themselves display as problematic or potentially problematic. Based on a corpus of archived chat reference transcripts, we show what types of problems in communication are displayed in the interaction, primarily through repair initiations, whether the problems are resolved, and, if so, how. Sources of problems that were targeted by both librarians and patrons included mistyping, typing in the wrong window, ambiguous terminology, differences in expertise between patrons and librarians, and the difficulty of giving and following instructions while not copresent. We conclude with implications for the training of future librarians in performing chat reference interactions.