Component based development is gaining popularity in the software engineering community. The reliability of components affects the reliability of the system. Different models and theories have been developed to estimate system reliability given the information about system architecture and the quality of the components. Almost always in these models a key attribute of component-based systems, the error propagation between the components, is overlooked and not taken into account in the reliability prediction.

We extend our previous work on Bayesian reliability prediction of component based systems by introducing the error propagation probability into the model. We demonstrate the impact of the error propagation in a case study of an automated Personnel Access Control System. We conclude that error propagation may have a significant impact on the system reliability prediction and, therefore, future architecture-based models should not ignore it.