Almost 40 to 57% of Enterprise Resource Planning (ERP) projects fail to realise any benefit, run over budget or time. Only a few published works explicitly focus on ERP Critical Success Factors (CSFs) in Make-to-Order (MTO) manufacturing small and medium size enterprises (SMEs). A dynamic Decision Support System (DSS) is developed for selecting and managing CSFs including production strategy and their interrelationships during and after completion of ERP projects in MTO SMEs. The research work carried out was based on a 30 month Knowledge Transfer Partnership (KTP) ERP implementation project. Based on the research objectives and the characteristics of the challenges facing the case company, action research method was assessed to be the most appropriate. Two Discrete Event (DE) simulation based DSS were developed. The first DSS studies the interrelationships of over thirty CSFs as an ERP system is being implemented. Users can determine the attributes of the CSF from real-time data and visualise the interrelationships of CSFs during phases of the ERP project. After the ERP system was implemented, a three stage DSS was developed to manage production strategy to realise benefits of ERP system. A prototype production planning and scheduling system (PPSS) using Microsoft Excel formed an ERP linkage for manufacturing lead-time analysis, Customer Relationship Management (CRM) activities and planning. The final stage involved managing the job release decisions based on Work Load Control (WLC) logic in purely manual assembly lines requiring high skill levels. This research contributes to limited research data available on managing ERP related CSFs in Make-to-Order (MTO) manufacturing firms. Also, a unified approach has ensured that a number of strategies that are not currently synchronised can be implemented successfully. The proposed methodology will enable small and medium size enterprises (SMEs) realise ERP benefits by focussing on CSFs during and after ERP implementation.