This research aims at describing errors as well as knowing the factors causing students to make an error in solving problems in the material of the Two-Variable Linear Equation System (SPLDV). This research involved 31 students from grade eight students of Indonesian junior high school. To collect the data, tests, observation, and interview methods were used. The data validity was triangulation in which it required a comparison of data with interviews. The technique of data analysis was in three stages, starting from data reduction, data presentation, and conclusion. The analytical framework was developed based on the Newman error category. The results obtained are three types of errors, namely error understanding problems, transformation errors, and process skills errors. Factors causing these errors, in general, are students who find difficulties to acknowledge the meaning of the questions, students have a low level of understanding and creativity in identifying problems into mathematical models, and students' carelessness in process skills.