Building up messages as a cognitive activity within the linguistic multi-level system is the result of the interaction between the various components of this system. Yet, this interactive process occurring in the language user's mind while encoding can vary from person to person. Likewise, it also differs in different recipients while decoding. This cognitively carried out difference in encoding can result in either unintended messages, though emptied out in mature and well-formed language constructions, or ill-formed ones. The present study aims at identifying the most frequent syntactic errors at the sentential level; and how immature or vague conceptualization manifests itself in the grammar-meaning relationship as reflected in the subjects' errors. Data were collected from the writings and the performance tests of mainly two Arab groups of third and fourth-year English majors in the course of Sociolinguistics at the University of Nizwa in the Sultanate of Oman. Errors were identified, classified and interpreted in terms of the underlying cognitive processes they went through during production. Errors were related to time-tense vague mapping, finite-nonfinite confusion, sentence-clause uncertainty, incorrect embedding, voice-related inaccuracy and verbless clauses or sentences.