Page must be specified before initializing for partial page render. - what causes this?

[John]

An unexpected application exception has occurred.
  a.. org.apache.tapestry5.ioc.internal.OperationException
  Page must be specified before initializing for partial page render.
    location
    classpath:epulse/audit/manager/pages/ManageUsers.tml, line 2015 </t:if> 
          16 <div 
          17 style="height:500px;width:240px;border:1px solid 
#ccc;overflow:auto;"> 
          18 <t:loop source="users" value="user"> 
          19 <t:actionlink t:id="clicker" t:zone="editZone" 
          20 t:context="user.userId" class="u">${user.username}</t:actionlink> 
          21 </t:loop> 
          22 </div> 
          23 </td> 
          24  
          25 <td valign="top"> 

    trace
      a.. Triggering event 'action' on ManageUsers:clicker
  b.. org.apache.tapestry5.runtime.ComponentEventException
  Page must be specified before initializing for partial page render.