The Workspace Manager java component is not installed. This page will not work properly. Make sure that the file 'wiki30-components-workspace-manager-<version>.jar' is present under the 'webapps/xwiki/WEB-INF/lib/' folder.
wiki30-components-workspace-manager-<version>.jar is not the right name
webapps/xwiki/WEB-INF/lib/ is only true for the all in one jetty distribution
XWIKI-8343Workspaces Manager does not work when installed with Extension Manager