Persistence IN WCF Workflow Service 4.0

I have created a WCF Workflow service in .NET 4.0.. How to implement persistence in it?

I have added following in web.config:

 <add name ="ConnStringPersistence" connectionString="Data Source=(local);Integrated Security=SSPI;Initial Catalog=SqlWorkflowInstanceStore;" providerName="System.Data.SqlClient"/>

<system.serviceModel>
    <behaviors>
      <serviceBehaviors>
        <behavior>

          <!-- To avoid disclosing metadata information, set the value below to false and remove the metadata endpoint above before deployment -->
          <serviceMetadata httpGetEnabled="true"/>

          <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="true"/>
          <sqlWorkflowInstanceStore connectionStringName="ConnStringPersistence"/>
          <workflowIdle timeToUnload="0"/>
        </behavior>

      </serviceBehaviors>
    </behaviors>
    <serviceHostingEnvironment multipleSiteBindingsEnabled="true" />
  </system.serviceModel>


When I add persist activity from toolbox, I get an entry in table  "InstancesTable" with exception "Persist activities cannot be contained within no persistence blocks."

How to solve it?