ERP systems which initially were developed for manufacturing organizations have in recent years spread to public sector organization. It is put forward that public sector organization differ from private organization and this might affect how successfully an ERP system is implemented. ERP systems are rarely studied in public sector organization and few researchers have explored the fit between ERP system and organizational structures. Therefore, the purpose of this paper is to explore what relationship that exists or do not exist between ERP system and organizational social structures in a military organization, and how this has affected the implementation and use. This is done through a qualitative case study of the Swedish Armed Forces with data from semi-structured interviews with 14 platoon commanders and 3 company commanders. The findings suggest that there is a misfit between the ERP system, PRIO, and the social structures in the organization which have made the implementation and use problematic. The technical shortcomings, such as the user interface, are not the main problem and employees might have been negative about the system anyway. This since platoon commanders and company commanders do not think platoon commanders are the best suited to do the tasks with PRIO.