State transitions in computer-integrated manufacturing (CIM) systems result either from the execution of the planned actions or from the occurrence of unpredictable events. One key requirement for task planning designed for CIM systems is the ability to monitor events and respond to them appropriately. Related issues include the specification and classification of possible system faults, errors and failures. The paper proposes an error-specification language, an error-monitoring mechanism and an error-recovery mechanism. Founded on a mathematical framework, the error-recovery mechanism uses the concept of severity to alter system characteristics. The paper presents some examples from an integrated multirobot system.