Hmm, I would click the reload button in Synaptic and try again. The 404 in the error message would lead me to believe that the site was offline for a bit when you were trying to install Evolution. I just went to the site and was able to download the deb manually, so the file is available.
All progress requires change, but not all change is progress.
--Henry Steele Commager
...there are some...who use change to promote their careers. And then there are those...who use their careers to promote change.