"The following packages have been held back..."

[Stephen Boulet <spboulet@speakeasy.net>]

I see the message in the subject header when doing apt-get upgrade, followed 
by a somewhat long list of packages. Can someone tell me what causes this? 

After running the upgrade command, I did an "apt-get install" on one of the 
packages that was in the list. It upgraded without a problem.

-- Stephen