Can't Delete Directory (Folder)

Sometimes when I try to delete a folder, it tells me I can't because it's being used by another program.  But it's NOT being used by any other program I have running.  What gives?

>>3
I had a folder named '4chan' within another folder of pictures.  I was reducing some of the pics in size and saving them to the 4chan folder so I could post them in /p/ without getting the image too big error (used IrfanView to reduce & save, in case that matters).  Anyhow, when I was done posting, I went to delete the 4chan folder, it gave me the in use error.  I used the cmd promt to del the files within the folder, but still couldn't delete the folder itself.

Funny thing, though, I simply renamed the folder from 4chan to 'asdf' and then deleted it without any problems.