When participants in reaction time (RT) tasks commit errors, the event-related brain potential (ERP) has been reported to show a negative-going deflection, the so-called error negativity (NE), followed by a positive-going component (PE). To examine the locus of NE within information processing and in order to test whether two successive P300 components are elicited in error trials, we manipulated the duration of perception- and response-related processing stages in visual and auditory spatial S-R compatibility tasks. Our results suggest that NE is closely coupled to motoric processes and elicited when information about the incorrectly executed response is available. The latency of the subsequent PE was influenced by perceptual as well as by response-related variables. Its scalp topography was not different from that of the P300 in correct trials and from a preceding positivity in incorrect trials. Therefore, we concluded that an additional error-related P300 is elicited by error events presumably relating to error recognition and the updating of the error context.