Note that server and root path are missing from the URL. I do have set github.com in the Spartacus plugin as source for both, File/Mirror location (XML metadata) and File/Mirror location (files). After going to the Spartacus setup and intuitively clicking Save these informational messages were displayed:The URL /additional_plugins/serendipity_event_spamblock_bayes/img/spamblock_bayes.load.gif?revision=1.9999 (IP ) could not be opened. Maybe the Serendipity or SourceForge.net Server is down - we are sorry, you need to try again later.
And subsequently the plugin upgrade worked.Deleting file package_template.xml...
Deleting file package_sidebar_en.xml...
Deleting file package_event_en.xml...
So it seems that the upgrade from 2.1.1 to 2.1.2 should had cleared those cache files. Probably manually removing templates_c/package_* should work as well.