The purpose of this study is to investigate the usability problems while using one of the applications of smart card, electronic purse with self service interfaces of NETMATIK. The usability problems of this self service interface were evaluated by heuristic evaluation and user trials.Two target groups, students and staffs, were involved in user trial. The average age for the first (younger) group was 18 while it was over 40 for the second (older) group. The problems that two target groups have encountered were evaluated seperately and the effect of age differences on problems has been explored whether it is the same for both target groups or not. The result of this study shows that both target groups had approximately same problems with the interface; however, these problems are more severe for the older groups. The common problems which both groups have with the interface are being timed out by the system, failing to enter password for card, failing to enter required password for e-purse. Implication for interface design is discussed.