In this blog and we will understand how to rectify QuickBooks Error 6129 0 for your QuickBooks. Before going on to the solutions, we will first analyze the symptoms and causes that lead to Error 6129. What does QuickBooks Error 6129 occur? QuickBooks Error 6129 can occur under different situations such as – During QuickBooks installation. During starting up of the Microsoft Windows or during the shutdown. During Microsoft Windows installation.