[xwiki-users] After update to 3.1 default skin is broken

Hello again, I updated my xwiki instance from 3.0 to 3.1. I deployed the new war-file and copied ?xwiki.cfg?, Xwiki.properties?, ?hibernate.cfg.xml? and ?mysql-connector-java-5.1.5-bin.jar? from the old instance. After die update the colibri-skin was broken. Any ideas what went wrong? Thank you again, Stephanie