I have been having some further thoughts on the matter of the Last.fm problem.
I downloaded the Last.FM Downloader.zip with a view to trying it out to download some music because it also includes artwork. I found that it would not work at all. There were tabs for Account and Login.
On the Last.FM Downloader.zip site I found this comment ......
"No user account or login is required in the United States, United Kingdom and Germany. All other users must create an Last.FM account"
My thought is that as you can access Last.fm and I cannot then perhaps your ISP is within the USA UK or Germany but my ISP is located outside this region and would require an account to login to Last.fm to download any artwork.
While doing this bit of research I found another rather interesting and excellent Album Cover Artwork download site ...www.album-cover-art.org