You should point the PLUG IN MANAGER to the exact folder which contains the DLL for the plug you are using.
 
I have used this to add new plugs and for some reason they tend to end up in some of the other available folder choices. For example they end up in nested folders with several other plugs so...... take a few seconds and look into all the folders available in the "audio plugins available". Some there are direct links and some go to folders with several plugs in them.
 
You need the 32bit plug. rescan. search for the plug. Open it from inside of MC.  
 
I have run Melodyne from inside MC4 w/o problems.
 
Keep us posted.