Professional and academic discourse is characterised by a specific phraseology, which usually poses problems for students. This paper investigates atypical verb+noun collocations in a corpus of English technical writing of Spanish students. I focus on the type of verbs that most frequently occurred in these awkward or questionable combinations and attempt to explore the reasons why the learners deviate from NS's norms. The analysis indicates that these learners tend to have problems with a set of sub-technical and high-frequency verbs. Deviant combinations involving these verbs are frequently the result of a deficient knowledge of the phraseology of academic and technical discourse. The unawareness of collocations that are typical of this discourse often leads students to create V+N combinations by relying on the "Open Choice Principle" (Sinclair, 1991) or by using patterns from their mother tongue. (Contains 3 notes and 2 tables.)