In Germany, dual apprenticeship contains two institutional learning locations: private enterprises and vocational schools. Around two-third of VET occurs on the job in companies. On-the-job-training (Tynjälä, 2008) is essential, because competencies are to be formed in practical work on the fundament of experience. Learning from errors at work can be conceptualized as a special form of experiential learning and thus, plays a crucial role in professional development (Gartmeier, et al., 2008). In order to achieve learning in working processes it should be allowed to produce errors (Bauer, et al., 2004). Within the VET apprentices need corresponding mentoring through trainers who have the ability to diagnose errors and deal with them in a pedagogically reasonable way. The effect from error management in enterprises correlates positive with the firm's performance (van Dyk et al., 2005). In spite of the relevance from apprenticeship in the workplace the current state of research, particularly the qualifications of trainers, can be described as a dark horse in German VET (Beck, 2005). The goal of this paper is to identify more about the workplace-learning-processes and at this point especially how do trainers think about learning from errors. Furthermore, it is fundamental how this thinking affects apprentices.