[vbat99]

I would delete all nfo's (nfo's only, not the artwork or actors (why download them again))Do a Refresh All in MC.
Then do a Search for new Movies

I've deleted the NFOs where there were duplicates.  Selected the "Search for new movies" they all came back up duplicate again and one or two of them that are dupes, won't even show anything in the main window of the program.  Not sure what the deal is?

Your other suggestions worked fine however.

In the General Filter, select Duplicates to show them.
Then go to Table View, Select Columns button, and ensure you have a check against fullpath and filename.
This will show where the duplicate files are and what they are called.