After defining the concept of error as it applies to Roentgen semiotics, we present a typology of the sources of semiotic error in clinical practice. It is a typology based on clinical observation, with the Peircean Categories and the triadic structure of Roentgen signs as organizing principles. This is followed by a review of a general psychological typology of the sources of human error. We conclude with the demonstration of a Category preserving correspondence between psychologic and semiotic sources of error. (...) Thus, independently derived and empirically based typologies of psychologic and semiotic error are shown to have the same categorical structure. (shrink)