Album Covers not showing v2.47b

When I select different filenames from my list of music, for some albums it displays the album cover and others it remains blank even though album art exists in the album folder. There seems to be no logical explanation. For example, I have two albums both with AlbumArtSmall.jpg. With one the album cover is displayed bottom left, on the other it remains blank. If I right click to add cover, the dialog box does not recognise any .jpg files in the folder.