iTunes album artwork issue...

This issue has only just come up due to myself and a flat mate having both bought new Macs and wanting to transfer music..

The scenario is the same for both of us.
I currently use the new iMac, and have now bought the aluminium MacBook for lectures and wandering around campus doing work situations. With migration assistant I was able to transfer everything obviously, which was great, so both of my computers are identical in every way.
The problem I'm having is that if I was to put music in to my iTunes library on my iMac, and then transfer it to the MacBook, the MacBook won't let me download the artwork; an error message pops up. This results in me having to use Google to find the image online.
My iTunes account is signed in on both of the computers all of the time so I'm guessing a reason for my problem could be that iTunes is registering that I've already downloaded the artwork and therefore won't let me do it again?!

Can anyone shed some light on this subject? Or suggest a way around it?

Many thanks.

I think you should ask it to Apple

Is all the artist and album title info entered correctly? If so, try this...

Go to album view. Select all albums (Ctrl-A). Right click (Ctrl-Click). Select get album artwork.

If the artist and album info is entered correctly, iTunes should send you the artwork regardless of where you got the songs from.

What does the error message say exactly?