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:
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
If this does not produce a Mogul plot, please 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 licence is activated.