Album artist missing: Windows media center requires songs in an audio album has the album artist declared to be properly shown in windows media center.
Album art missing: Again, to be properly shown in windows media center, album art has to be downloaded into your folder.
Audio files have different locations: If files are not stored in the same album folder, the album art can sometimes show the wrong picture.
All these problems (and more) takes Album art fixer care of. Album art fixer retrieves all your albums from your library so you can decide what and how to fix these problems within Album art fixer.