The purpose of the article is to identify difficulties in using advanced technologies in the implementation of projects and their causes, taking the size of enterprises into account. Analysis of the difficulties in using advanced technologies, which occurred during implementation of projects, and of their causes, was carried out, based on a research questionnaire which was administered online and in which 787 business entities participated. The size of enterprises was taken into account in the research study. Using advanced technologies causes a number of difficulties in business practice. Findings of the research study identify types of these difficulties and give their causes. The conclusions that were drawn from the study enable attention to be drawn special to the most problematic areas of business activities connected with implementing projects with the use of advanced technologies. This research paper offers a new classification of advanced technologies as well as of their causes. The paper identifies and classifies not only the technologies, the types of enterprises (according to their size), but also the most frequent causes of the difficulties which occur during implementation of projects. This allows us to focus on the areas of activities which are most prone to difficulty occurrence.