Interfacing device visa USB in MATLAB using C DLL

Question

I am doing a project in which i have to interface a device via USB using MATLAB. The API (dll files) of the device is written in the C++ so i used loadlibrary command in MATLAB to load it and done interfacing. It's working fine. The problem is that when i run the program from MATLAB it works fine but for running it again i need to plug out the device and then plug in to make it run successfully. But i wrote a C++ interface that is working fine. Can anyone tell me what should i do? The problem seems to be of getting the handle of the device but i am not getting the true point.