Today the amount of web applications has grown exponentially and the number of both novice and experienced users decided to experiment with these applications has increased. However, there has been a large increase in problems when the user interacts with those applications. Therefore, a study was made in order to ensure the quality of web applications. To achieve this, a usability methodology for transactional web applications was applied first, where a considerable number of problems identified by Nielsen principles were found and we applied the communicability methods SIM (Semiotic Inspection Method) and CEM (Communicability Assessment Method). During this research a web app was tested, we found out that there is an association with usability problems, where the 72% of these problems are about communicability, which turn to be the most serious problems. This shows how difficult is for the designer to interact with the user and vice versa.