This research explored the most common writing errors of Science and Arts students of the Foundation year program at a Saudi University that hinder them from achieving their course goals, learning outcomes and becoming efficient writers. The importance of this research stems from the fact that, it is a comparative study that shows the differences in writing errors between Science and Arts students and relates writing difficulties to students' background education, family support, level of the language and teacher's feedback techniques. It unveils the causes of writing errors and suggests suitable remedies from teacher's perspectives. The findings can be useful for teachers, students and course designers.