I'm not strong on QoS, but I did see in the 12.4T documentation where the policy can be suspended if you've configured a guarantee that exceeds the available BW. See
http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/qos_mqc_ps6441_TSD_Products_Configuration_Guide_Chapter.html. You might also search for troubleshooting guides in general.