The basis of this study was to explore the perceptions of Revenue Staff regarding the factors that influenced their decision to adopt a new knowledge management system. Using a post-positivist case study approach the study examined staff perceptions of change management processes, communication styles, training application and the compatibility of the knowledge management system to work practices. The literature review explored the elements of change management in public sector organisations, as well as change theory, and online training design theory. A post-positivist case study approach using qualitative methods was used as the research methodology to explore the perceptions of staff to the implementation of NASC. The research design utilised Qualtrics, a web-based survey tool, administered to representative samples of Revenue staff. The design was an exploratory case study and the collection of qualitative data in this research involved language and was abductive, using a process of moving back and forth between inductive and deductive analysis and using specific observations, evidence and patterns gathered from the research to make broad conclusions. The research was divided into two phases and focused on two separate cohorts of staff who were undergoing introductory training to NASC during the timeline of this research. The findings of this study suggest that the perceptions of Revenue Staff are complex and dependent on many variables that include leadership and communication styles as well as effective change management techniques. The findings also suggest that good online training design enhanced positive perceptions of the NASC system. This study contributes to the literature on change in public service organisations in Ireland. It confirms that good change management theory, positive communication and good online training design be explicit features of the introduction and rollout of IT systems, and that these features be supported by all levels of the organisation