mp3 icon preview not working in OS X Lion

Dear All,

I have an issue with the icon preview for ".mp3" files in OS X LION.

Pdf's, photoes, videos are previed fine, but certain of my mp3 files have turned into an icon that displays the iTunes logo. These icons can only be previewed in column view, and if I use the "Get info" command. If I highlight the file and press Space, they play allright. They play in iTunes. Strangely enough, not all the mp3's on my mac have lost this feature. Some files still retain the ability of icon preview. But when I copy them to another location, icon preview is not accessible, and the file icon displays the iTunes logo (album artwork is not displayed either in case of copying said files). Please, see some photoes below:

(1) Some mp3 file icons are still previewable:

(2) The others are not (even in the same folder):

(3) They are previewable in the "Get info" window:

(4) They cannot be previewed in the Cover Flow view:

In the Finder view options, I have "Show icon preview" checked. I have the latest version of iTunes (10.5.2).

May be, like in OS Snow Leopard, I have to delete the "com.apple.finder.plist" file in the Library/Preferences folder.

But when I get to the Preferences folder, I cannot delete the plist files, since there is no option "Move to trash" in the contextual menue (right mouse click).

Moreover, there are about 20 files "com.apple.finder.plist" with a different date.

Please, help me resolve this issue and return the mp3 file icon preview fuctionality to my Mac.

Thank you in advance.