Dynamic copyies: the "Copies" action menu (which launch a pop on the source of a linked copy) does not work any more

I made a linked copy on the same site from one double page to another double page. When going to the source page and clicking on the action menu, I have a "Copies" action menu (which launches a pop with all linked copies) + a quick list of most recent copies....

The pop-up does not work any more and fires an exception:

2007-10-10 13:30:59,954: INFO [org.jahia.bin.Jahia] - Processed [/jahia/Jahia/site/test/op/edit/pid/31] user=[root] ip=[127.0.0.1] in [344ms]
2007-10-10 13:31:14,454: INFO [org.jahia.bin.Jahia] - Processed [/jahia/Jahia/site/test/op/edit/pid/7] user=[root] ip=[127.0.0.1] in [453ms]
2007-10-10 13:31:25,845: ERROR [org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/jahia].[org.jahia.jsp.jahia.war.jsp.jahia.engines.importexport.dispPickers_jsp]] - "Servlet.service()" pour la servlet org.jahia.jsp.jahia.war.jsp.jahia.engines.importexport.dispPickers_jsp a gΘnΘrΘ une e
xception
java.lang.NullPointerException
at org.jahia.data.fields.JahiaDateField.load(JahiaDateField.java:117)
at org.jahia.services.fields.JahiaFieldBaseService.loadField(JahiaFieldBaseService.java:836)
at org.jahia.services.fields.JahiaFieldBaseService.loadField(JahiaFieldBaseService.java:775)
at org.jahia.services.fields.JahiaFieldBaseService.loadField(JahiaFieldBaseService.java:675)
at org.jahia.services.fields.JahiaFieldBaseService$$FastClassByCGLIB$$a23200ff.invoke(<generated>)
at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:149)
at org.springframework.aop.framework.Cglib2AopProxy$CglibMethodInvocation.invokeJoinpoint(Cglib2AopProxy.java:661)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:122)
at org.springframework.aop.interceptor.AbstractTraceInterceptor.invoke(AbstractTraceInterceptor.java:80)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:144)
at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:606)
at org.jahia.services.fields.JahiaFieldBaseService$$EnhancerByCGLIB$$796a971e.loadField(<generated>)
at org.jahia.content.ContentObject.getMetadataAsJahiaField(ContentObject.java:1502)
at org.jahia.content.ContentObject.getMetadataAsJahiaField(ContentObject.java:1481)
at org.jahia.content.ContentObject.getMetadataValue(ContentObject.java:1519)
at org.jahia.jsp.jahia.war.jsp.jahia.engines.importexport.dispPickers_jsp._jspService(dispPickers_jsp.java:448)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.jahia.bin.filters.esi.ESIFilter.doFilter(ESIFilter.java:110)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:432)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Thread.java:619)