If you use Dotdeb with Debian Squeeze you should check your dotdeb repository config. If you have this:
deb http://packages.dotdeb.org stable all deb-src http://packages.dotdeb.org stable all
And you want to continue with Squeeze for now, you need to edit the dotdeb config to:
deb http://packages.dotdeb.org squeeze all deb-src http://packages.dotdeb.org squeeze all
Or you'll encounter issues updating/installing dotdeb packages on Squeeze. Wheezy is now "stable".