This study presents an error analysis on an adult Nigerian postgraduate student in the United Kingdom. The results reveal that there are a lot of errors which associated with both Interlingua and intralingua. His second language development moves at lower rate. However, in some instances he has been using appropriate aspects of target language; that at certain points he realises inappropriate use of target language and makes self-correction. In terms of teaching implication, some errors can be corrected immediately while others can be delayed because too much negative feedback may hinder the progress of the learner. For example, the omission of /s/ sound can be ignored for immediate correction because it is often unnoticed, whereas errors associated with unmarked verb form can be corrected immediately.
Keywords: Error Analysis, Inter-language, Interlingua, Intralingua, Nigeria, Postgraduate Students, Second Language Acquisition