The filename isn't being renamed
Click the
pop-up menu, and make sure you have either selected a) “Filename” if you only want to rename the filename but not the file ending, or b) “Filename and Suffix” if you want to rename the filename and its ending. For Find & Replace make sure that if you’re using any of the characters *, ?, +, ( or ) in your find text that “Regular expression” is deselected.