Null exception in faces renderkit - jsf

Question

I get the following exception when I click a button on a JSF/RichFaces page.
This problem only seems to happen on one server. Any ideas?
StandardWrapperValve[Faces Servlet]: PWC1406: Servlet.service() for servlet Faces Servlet threw exception
java.lang.NullPointerException
at com.sun.faces.renderkit.html_basic.MenuRenderer.getCurrentSelectedValues(MenuRenderer.java:633)
at com.sun.faces.renderkit.html_basic.MenuRenderer.renderOption(MenuRenderer.java:524)
at com.sun.faces.renderkit.html_basic.MenuRenderer.renderOptions(MenuRenderer.java:757)
at com.sun.faces.renderkit.html_basic.MenuRenderer.renderSelect(MenuRenderer.java:811)
at com.sun.faces.renderkit.html_basic.MenuRenderer.encodeEnd(MenuRenderer.java:335)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:836)
at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:279)
at com.sun.faces.renderkit.html_basic.GridRenderer.encodeChildren(GridRenderer.java:242)
at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:812)
at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:271)
at com.sun.faces.renderkit.html_basic.GridRenderer.encodeChildren(GridRenderer.java:242)
at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:812)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:886)
at javax.faces.render.Renderer.encodeChildren(Renderer.java:137)
at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:812)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:886)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:892)
at com.sun.faces.application.ViewHandlerImpl.doRenderView(ViewHandlerImpl.java:245)
at com.sun.faces.application.ViewHandlerImpl.renderView(ViewHandlerImpl.java:176)
at org.ajax4jsf.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:100)
at org.ajax4jsf.application.AjaxViewHandler.renderView(AjaxViewHandler.java:176)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:106)
at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:251)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:144)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:245)
at org.apache.catalina.core.ApplicationFilterChain.servletService(ApplicationFilterChain.java:427)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:333)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
at org.ajax4jsf.webapp.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:178)
at org.ajax4jsf.webapp.BaseFilter.handleRequest(BaseFilter.java:290)
at org.ajax4jsf.webapp.BaseFilter.processUploadsAndHandleRequest(BaseFilter.java:368)
at org.ajax4jsf.webapp.BaseFilter.doFilter(BaseFilter.java:495)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:246)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:313)
at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:287)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:218)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:648)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:593)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:94)
at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:98)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:222)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:648)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:593)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:587)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1096)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:166)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:648)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:593)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:587)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:1096)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:288)
at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.invokeAdapter(DefaultProcessorTask.java:647)
at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.doProcess(DefaultProcessorTask.java:579)
at com.sun.enterprise.web.connector.grizzly.DefaultProcessorTask.process(DefaultProcessorTask.java:831)
at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.executeProcessorTask(DefaultReadTask.java:341)
at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.doTask(DefaultReadTask.java:263)
at com.sun.enterprise.web.connector.grizzly.DefaultReadTask.doTask(DefaultReadTask.java:214)
at com.sun.enterprise.web.connector.grizzly.TaskBase.run(TaskBase.java:265)
at com.sun.enterprise.web.connector.grizzly.ssl.SSLWorkerThread.run(SSLWorkerThread.java:106)
here's the page causing the problem:
<h:form id="clientCreatorForm" >
<h1><h:outputText value="Linguist Creator"/></h1>
<rich:messages styleClass="error_msg" showDetail="true" showSummary="true"/>
<h:panelGrid id="op" columns="2">
<rich:spacer height="20px" />
<h:outputText value="" />
<h:outputText value="Linguists:" />
<rich:comboBox value="#{linguistCreator.linguistCompanyName}">
<f:selectItems value="#{linguistCreator.companyItemsAvailable}" />
<a4j:support action="#{linguistCreator.l1RequiredInputTest}"
ajaxSingle="true"
event="onselect"
reRender="footerPanel" />
</rich:comboBox>
</h:panelGrid>
<rich:spacer height="20px" />
<h:panelGrid id="footerPanel" columns="1" >
<a4j:commandButton id="updatebutton" value="Add new Language(s) to selected linguist."
action="#{linguistCreator.retrieveLinguistObjects}"
disabled="#{linguistCreator.enterDisabledL1}"/>
<a4j:commandButton id="addButton" value="Add new linguist" action="linguist2" />
</h:panelGrid>
</h:form>