In today''s manufacturing environment, different parts manufactured in-house and bought from suppliers are often assembled together into a finished product. Competition has made it important for companies to deliver a customized product on a promised date. However, when inventory items are missing at the time of production, lead times for products become uncertain and this makes it difficult to fulfill a customer order on the promised date. It is thus important to explore the causes of missing items at the time of production in order to solve such a problem. The questions at issue have been what the causes of the problem of missing items are and how to effectively reduce the problem. The sources of the problem have been the result of the work procedure, the in-house developed ERP system, stealing from orders, ineffective barcode scans, re-sequencing at the component manufacturing department, set-up times at the component manufacturing department and human errors among others. The suggestions: modification of the work procedure and the underlying software used at work, increasing effective scanning and using some checks at critical points in the material flow.