Object reference not set to an instance of an object

[ComptonAlvaro]

I have Visual studio 2015 community, I have installed the last version of vsix, later I have installed OpenVpn from nugets and finally I dowonload NUnit, the last version, which exe is nunit3-console.exe.

In visual studio, in options of OpenCover, I have set the path to NUnit (nunit3-console.exe) and for the openvocer-console.exe file.

I right click in one of my tests methods in the openCover explorer window, and I get the error Object reference not set to an instance of an object.

What does it mean? How could I solve this problem?

Thanks.