In this study, we propose to shed light on the origin of lexical errors in the written productions of Algerian students enrolled in French language license. Using typologies of lexical errors from explanatory and Combinatorial Lexicology, an error analysis was carried out of 68 texts written an examination situation. The results revealed a dominance of formal and morphosyntactic errors. The ignorance of the forme of the lexical unit or of one of its morphosyntactic properties, the analogy of constructions and the interference constitute the most advanced hypotheses in order to explain the deviant forms noted.