When you debug an NX Open application using Visual Studio, you compile and link the app using visual studio this way:
Project-->Properties-->Debug-->Start External Program <Path to NX executable>
The problem is that this NX is not the NX that is linked to Teamcenter. To use the NX that is linked to Teamcenter you have to launch the NX from the Teamcenter interface. This is because I want to use parts stored in Teamcenter in my NX Open App.