easy peasy soloing

Soloed Problim earlier this week and Attumen was easier than ever.  My next soloing challenge, however slight, was to solo Ossirian.  This wasn't too bad, there really wasn't any point other than i saw that the Armory said that i had never killed him.  The irony?  He drops a head that starts a quest; as it turned out, i couldn't accept that quest because i had already completed it.

eta: It's been five days and the armory still says I've never downed Oss. I have no idea what is causing the error.