The proper way of linking Mogul to MOE would be through the Mogul setup panel.
Here are the steps:
1- Start MOE.
2- Build a small molecule.
3- Select a dihedral
4- In the MOE menu, choose MOE | Compute | Conformations | Mogul Analysis
5- Press the gear icon and browse to Mogul binary:
C:/Program Files (x86)/CCDC/CSD_2018/Mogul/mogul.exe
6- Specify your MOGUL options ("include bond lengths", "include bond angles", etc..).
7- Press OK to close the configuration panel
8- Press RUN to see the Mogul plot
I would also try to run Mogul by clicking on the desktop icon or Start Menu icon (Windows) to verify that it is properly installed and that the license is activated.