Sometimes the GeoServer home UI (only for some instances in the cluster) informs the user about problems while loading the quota store. The issue seems to be related to an unique constraint violation during the TILESET record creation (attached to the JIRA a fragment of the GeoServer's log file).
Linux OpenSUSE 12.3 64bit
Apache Tomcat: 6.0.41
Cluster of GeoServer 2.4.8 with shared data_dir
Shared GWC's disk quota configured in Oracle DB
Fixed in GWC
Mass closing all resolved issues not modified in the last 4 weeks