Itunes won't open/play/import a mp3 file.


Duplicate file

Check if the mp3 or a file with same name is not already in the library.

Wrong fileformat

Make sure the file is a real mp3 file and not an incompatible file named .mp3
Make sure the file extension is correct for its type.

Change ID3 tag

Certain ID3 tags (IDv3 2.4, APEv2) in the mp3 can cause Itunes to fail loading it.
Remove the Tag using a mp3 editor. You can do with winamp, push alt-3 with the file in winamp selected and uncheck the include tag in file box.