When Ur&Penn decided to leave Microsoft Dynamics NAV after 14 years, most called us “ambitious” for building our own ERP from scratch. As the lead engineer responsible for this migration, I designed a hybrid architecture that eliminated the limitations of off-the-shelf solutions while preserving years of business-critical data. This is the untold technical story of how we successfully migrated a complex retail operation serving the Nordic region to a custom ERP system—without disrupting daily operations. I’ll share the architecture decisions, migration strategies, and unexpected challenges that shaped our journey away from NAV toward a solution perfectly tailored to our unique retail needs.