I'm not sure if this is a bug, or a game mechanic I do not understand, but I am currently at war with the Magnar and I cannot capture their outposts or attack their cities.  This new war follows shortly after a previous war where I could capture their holdings.  Is there a spell or ability that could prevent my assault?  Does it have something to do with going to war again so soon after a previous war?  If it is a bug, it is definitely a game killer (at least for this current game) as the locations I'm trying to capture are of vital strategic importance.  Has anyone else encountered this, and if it is a bug, is there a fix planned?