genesys8.0 when retrieveMultipleObjects cause a ConfigException

[pplppo1314]

Hey guys!
when i connect to configserver to retrieveMultipleObjects , it throw an exception like this :[color=red]com.genesyslab.platform.applicationblocks.com.ConfigException：There are not enough object paths in the Read request result[/color], what does it mean? how to deal with it ?

my code as followed :

cfgAgentGroupQuery query = new CfgAgentGroupQuery ();
query.setState ( CfgObjectState.CFGEnabled );
Collection<CfgAgentGroup> collection = m_cfgService.retrieveMultipleObjects ( CfgAgentGroup.class, query );

it's weird that the same codes it works before.
thanks!