Though hospitals managers wish to have a unified medication system, physicians continue double registration of prescriptions. The traditions of prescribing both electronically and on paper, as well as the power of the medical record are some of the disregarded elements when introducing a computerized physician order entry system (CPOE). The result is that the explicit goal to eliminate double registrations is not fulfilled. The pattern of prescriptions continues unchanged and CPOE replaces the abandoned paper based medication card. In this case study a symmetric approach reveals how double registrations on one hand are considered a safety problem, but on the other hand double registrations intercept and prevent medication errors. Keywords. Computerized physician order entry system, CPOE, medication errors, Actor network, evaluation, organisational change, communication.