Agents can't access any resources due to missing classloader

Issue

When trying to start the agent we get the following errors:

2012-05-24 08:16:36,234 ERROR [main] (rhq.core.pc.inventory.InventoryManager)- Access to resource [Resource[id=10421, type=Linux, key=resource.key, name=resource.name, parent=<null>, version=Linux 2.6.18-274.3.1.el5]] will fail due to missing classloader!
org.rhq.core.clientapi.agent.PluginContainerException: Failed to obtain classloader for resource: Resource[id=10421, type=Linux, key=resource.key, name=resource.name, parent=<null>, version=Linux 2.6.18-274.3.1.el5]
        at org.rhq.core.pc.plugin.PluginComponentFactory.getResourceClassloader(PluginComponentFactory.java:212)
        at org.rhq.core.pc.inventory.InventoryManager.initResourceContainer(InventoryManager.java:1426)
        at org.rhq.core.pc.inventory.InventoryManager.processSyncInfo(InventoryManager.java:2526)
        at org.rhq.core.pc.inventory.InventoryManager.synchInventory(InventoryManager.java:1027)
        at org.rhq.core.pc.inventory.InventoryManager.handleReport(InventoryManager.java:1001)
        at org.rhq.core.pc.inventory.InventoryManager.activateAndUpgradeResources(InventoryManager.java:2809)
        at org.rhq.core.pc.inventory.InventoryManager.initialize(InventoryManager.java:232)
        at org.rhq.core.pc.PluginContainer.startContainerService(PluginContainer.java:431)
        at org.rhq.core.pc.PluginContainer.initialize(PluginContainer.java:282)
        at org.rhq.enterprise.agent.AgentMain.startPluginContainer(AgentMain.java:1888)
        at org.rhq.enterprise.agent.AgentMain.start(AgentMain.java:649)
        at org.rhq.enterprise.agent.AgentMain.main(AgentMain.java:419)
Caused by: org.rhq.core.clientapi.agent.PluginContainerException: [Warning] Missing parent resource for resource=Resource[id=10421, type=Linux, key=resource.key, name=resource.name, parent=<null>, version=Linux 2.6.18-274.3.1.el5]
        at org.rhq.core.clientapi.agent.PluginContainerException.wrapIfNecessary(PluginContainerException.java:69)
        at org.rhq.core.clientapi.agent.PluginContainerException.<init>(PluginContainerException.java:96)
        ... 12 more

And after that the missing classloader error for every resource.