Two problems, both from Gaspar Nicolas' "Tratado da Prática d'Arismética", published in 1519 are considered in this study. The tasks were carried out using pencil, paper and students from Portuguese schools. The aim was to explore the following students' performances: 1. The students were able to recognize the "error", explaining it by using a coherent procedure. 2. The students argued why this answer is wrong/incomplete. 3. The solutions of some students present a good concept and clarity of procedure, compared to aspects omitted in historical literature. 4. The students understood the importance of knowing the "errors" made by famous mathematicians in two related aspects: mathematics is a human activity prone to errors and, consequently, the fear of making errors should not be an obstacle to learning math at school.