Why will iTunes not Download some Album Artwork?

I realize this is a really noob question, but I promise I have exhausted every option I have thought of, short of calling cupertino directly.

So, this is situation is as follows:

I upgraded to Lion and right in the middle of the process my house lost power, and my laptop only had 4% batt left. I basically had to start over and wipe the HD becasue of widespred currpution. no worries though because I have everything backed up. So everything came back perfectly, but when copying my Music back from the external to my local HD I noticed the itunes was tasked with redownloading the artwork. 75% showed right back up, but the are several albums (purchased for, Itunes that refuse to download, i have double and tripple check track and artist names. any ideas? SHort of manually finding these covers, how do i get the "Automatic" back in iTunes?

thanks in Advance