This week, the SourceForge.Net servers have been attacked. Since the Serendipity project hosts files and our plugin's CVS on SourceForge's provided servers, this also affects our maintaineance and distribution of plugins through Spartacus.
For people having problems, you can manually download plugins through spartacus.s9y.org. You should be able to choose netmirror.org as the spartacus mirror as well.
Normal services should be restored in a few days. For the longer run, our team might move plugin repositories from CVS to SVN or even Git, but changing this will take some time (and discussion).