Not all music in itunes library will sync with my ipod touch

I have just had the ios 8.4 upgrade added at an Apple store after they had had to reset my ipod touch (64GB). I have downloaded a new cd and synced all the library but although the new album has transferred over I am still missing some albums. They show in my library on my laptop but when I click on them they say the pc is not authorised to play them. I follow the instructions to authorise it but continually get the following error message

"We could not complete your iTunes store request, an unknown error occurred -45054. There was an error in the iTunes store please try later"

I am using Windows 7

Can anyone help please?

Thanks