You might check for the same filename as earlier, only with ._ (dot underscore) in front of it. You might well have to go into the Terminal to do this. Open Terminal.app in the Applications->Utilities folder, drag the folder containing the problem files to the terminal app. If you must do this from SUM, then I suppose you know where the path is located anyway.
This will list the path to the folder in question in the terminal. Back the cursor to the front of the line and type "ls -a " so that the line looks like:
ls -a /some/path
You should see a listing of every file in that directory. Now look for those "._" files. If you see a file of the same name with "._" in front, you might try to remove it by typing:
rm -i ._filename*
where filename is the first unique part of the filename relative to every other similar file in the directory. You will be prompted to delete the file. If you see any other files listed than the one you want to delete, type "n" at the prompt.