Exception does not point to the class that is missing Serializable

This is the stack dump:

Sadly the UserSession needs to implements Serializable, yet no clue of the class is given in the below error message. I have included the Project.

15:05:47,044 INFO [org.jboss.as.osgi] (MSC service thread 1-6) JBAS011943: Unregister module: Module "deployment.jb225-lab-3-3.war:main" from Service Module Loader
15:05:47,047 INFO [org.jboss.as.server.deployment] (MSC service thread 1-8) JBAS015877: Stopped deployment jb225-lab-3-3.war in 4ms
15:05:47,048 INFO [org.jboss.as.server.deployment] (MSC service thread 1-8) JBAS015876: Starting deployment of "jb225-lab-3-3.war"
15:05:47,060 INFO [org.jboss.weld.deployer] (MSC service thread 1-8) JBAS016002: Processing weld deployment jb225-lab-3-3.war
15:05:47,065 INFO [org.jboss.weld.deployer] (MSC service thread 1-2) JBAS016005: Starting Services for CDI deployment: jb225-lab-3-3.war
15:05:47,066 INFO [org.jboss.as.osgi] (MSC service thread 1-3) JBAS011941: Register module: Module "deployment.jb225-lab-3-3.war:main" from Service Module Loader
15:05:47,067 INFO [org.jboss.weld.deployer] (MSC service thread 1-6) JBAS016008: Starting weld service for deployment jb225-lab-3-3.war
15:05:47,093 ERROR [org.jboss.msc.service.fail] (MSC service thread 1-6) MSC000001: Failed to start service jboss.deployment.unit."jb225-lab-3-3.war".WeldService: org.jboss.msc.service.StartException in service jboss.deployment.unit."jb225-lab-3-3.war".WeldService: org.jboss.weld.exceptions.DefinitionException: WELD-000072 Managed bean declaring a passivating scope must be passivation capable. Bean: Managed Bean [class scopes.web.UserSession] with qualifiers [@Any @Default]
at org.jboss.as.weld.services.WeldService.start(WeldService.java:83)
at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1811) [jboss-msc-1.0.2.GA-redhat-1.jar:1.0.2.GA-redhat-1]
at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1746) [jboss-msc-1.0.2.GA-redhat-1.jar:1.0.2.GA-redhat-1]
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) [rt.jar:1.6.0_29]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) [rt.jar:1.6.0_29]
at java.lang.Thread.run(Thread.java:662) [rt.jar:1.6.0_29]
Caused by: org.jboss.weld.exceptions.DefinitionException: WELD-000072 Managed bean declaring a passivating scope must be passivation capable. Bean: Managed Bean [class scopes.web.UserSession] with qualifiers [@Any @Default]
at org.jboss.weld.bean.ManagedBean.checkType(ManagedBean.java:406)
at org.jboss.weld.bean.AbstractBean.initializeAfterBeanDiscovery(AbstractBean.java:150)
at org.jboss.weld.bean.AbstractClassBean.initializeAfterBeanDiscovery(AbstractClassBean.java:184)
at org.jboss.weld.bean.ManagedBean.initializeAfterBeanDiscovery(ManagedBean.java:362)
at org.jboss.weld.bootstrap.BeanDeployment.doAfterBeanDiscovery(BeanDeployment.java:229)
at org.jboss.weld.bootstrap.BeanDeployment.afterBeanDiscovery(BeanDeployment.java:221)
at org.jboss.weld.bootstrap.WeldBootstrap.deployBeans(WeldBootstrap.java:366)
at org.jboss.as.weld.WeldContainer.start(WeldContainer.java:82)
at org.jboss.as.weld.services.WeldService.start(WeldService.java:76)
... 5 more

15:05:47,299 INFO [org.jboss.as.osgi] (MSC service thread 1-1) JBAS011943: Unregister module: Module "deployment.jb225-lab-3-3.war:main" from Service Module Loader
15:05:47,301 INFO [org.jboss.as.server.deployment] (MSC service thread 1-6) JBAS015877: Stopped deployment jb225-lab-3-3.war in 3ms
15:05:47,302 INFO [org.jboss.as.server.deployment] (MSC service thread 1-4) JBAS015876: Starting deployment of "jb225-lab-3-3.war"
15:05:47,302 INFO [org.jboss.as.server] (DeploymentScanner-threads - 2) JBAS015863: Replacement of deployment "jb225-lab-3-3.war" by deployment "jb225-lab-3-3.war" was rolled back with failure message {"JBAS014671: Failed services" => {"jboss.deployment.unit.\"jb225-lab-3-3.war\".WeldService" => "org.jboss.msc.service.StartException in service jboss.deployment.unit.\"jb225-lab-3-3.war\".WeldService: org.jboss.weld.exceptions.DefinitionException: WELD-000072 Managed bean declaring a passivating scope must be passivation capable. Bean: Managed Bean [class scopes.web.UserSession] with qualifiers [@Any @Default]"}}
15:05:47,315 INFO [org.jboss.weld.deployer] (MSC service thread 1-5) JBAS016002: Processing weld deployment jb225-lab-3-3.war
15:05:47,320 INFO [org.jboss.weld.deployer] (MSC service thread 1-8) JBAS016005: Starting Services for CDI deployment: jb225-lab-3-3.war
15:05:47,322 INFO [org.jboss.as.osgi] (MSC service thread 1-8) JBAS011941: Register module: Module "deployment.jb225-lab-3-3.war:main" from Service Module Loader
15:05:47,322 INFO [org.jboss.weld.deployer] (MSC service thread 1-1) JBAS016008: Starting weld service for deployment jb225-lab-3-3.war
15:05:47,349 ERROR [org.jboss.msc.service.fail] (MSC service thread 1-1) MSC000001: Failed to start service jboss.deployment.unit."jb225-lab-3-3.war".WeldService: org.jboss.msc.service.StartException in service jboss.deployment.unit."jb225-lab-3-3.war".WeldService: org.jboss.weld.exceptions.DefinitionException: WELD-000072 Managed bean declaring a passivating scope must be passivation capable. Bean: Managed Bean [class scopes.web.UserSession] with qualifiers [@Any @Default]
at org.jboss.as.weld.services.WeldService.start(WeldService.java:83)
at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1811) [jboss-msc-1.0.2.GA-redhat-1.jar:1.0.2.GA-redhat-1]
at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1746) [jboss-msc-1.0.2.GA-redhat-1.jar:1.0.2.GA-redhat-1]
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) [rt.jar:1.6.0_29]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) [rt.jar:1.6.0_29]
at java.lang.Thread.run(Thread.java:662) [rt.jar:1.6.0_29]
Caused by: org.jboss.weld.exceptions.DefinitionException: WELD-000072 Managed bean declaring a passivating scope must be passivation capable. Bean: Managed Bean [class scopes.web.UserSession] with qualifiers [@Any @Default]
at org.jboss.weld.bean.ManagedBean.checkType(ManagedBean.java:406)
at org.jboss.weld.bean.AbstractBean.initializeAfterBeanDiscovery(AbstractBean.java:150)
at org.jboss.weld.bean.AbstractClassBean.initializeAfterBeanDiscovery(AbstractClassBean.java:184)
at org.jboss.weld.bean.ManagedBean.initializeAfterBeanDiscovery(ManagedBean.java:362)
at org.jboss.weld.bootstrap.BeanDeployment.doAfterBeanDiscovery(BeanDeployment.java:229)
at org.jboss.weld.bootstrap.BeanDeployment.afterBeanDiscovery(BeanDeployment.java:221)
at org.jboss.weld.bootstrap.WeldBootstrap.deployBeans(WeldBootstrap.java:366)
at org.jboss.as.weld.WeldContainer.start(WeldContainer.java:82)
at org.jboss.as.weld.services.WeldService.start(WeldService.java:76)
... 5 more

15:05:47,353 INFO [org.jboss.as.controller] (DeploymentScanner-threads - 2) JBAS014774: Service status report
JBAS014777: Services which failed to start: service jboss.deployment.unit."jb225-lab-3-3.war".WeldService: org.jboss.msc.service.StartException in service jboss.deployment.unit."jb225-lab-3-3.war".WeldService: org.jboss.weld.exceptions.DefinitionException: WELD-000072 Managed bean declaring a passivating scope must be passivation capable. Bean: Managed Bean [class scopes.web.UserSession] with qualifiers [@Any @Default]