Groups field in Windows Active Directory doesn't get updated

Question

Hello IDM Experts,
I am trying to append one more group to a few hundred users in AD. When I run the below code, I am not getting any error and at the same time the groups field in AD doesn't seem to get updated either. Any thoughts? Thanks!
<Activity id='1' name='CheckOut'>
  <Action id='0' name='Check Out AD' application='com.waveset.session.WorkflowServices'>
    <Argument name='op' value='checkoutView' />
    <Argument name='type' value='User' />
    <Argument name='id' value='$(userId)' />
    <Argument name='authorized' value='true' />
    <Argument name='subject' value='Configurator' />
    <Argument name='Form' value='Empty Form'/>
    <Return from='view' to='userview' />
  </Action>
  <Action id='2' name='Change AD Values'>
    <expression>
      <block>
        <append name='userview.accounts[Sample Domain].groups'>
          <s>CN=grp_ext_owner,OU=Task Groups,OU=Groups,DC=sample,DC=com</s>
        </append>
        <ref>userview.accounts[Sample Domain].groups</ref>
      </block>
    </expression>
  </Action>
  <Action id='3' name='Check In AD' application='com.waveset.session.WorkflowServices'>
    <Argument name='op' value='checkinView' />
    <Argument name='view' value='$(userview)' />
    <Argument name='authorized' value='true' />
    <Argument name='subject' value='Configurator' />
  </Action>
  <Transition to='end' />
</Activity>

Answer 1

Some ideas...
1) Do you have a mapping of the groups attribute in your Sample Domain resource adapter? One element should read similar to:
<AccountAttributeType id='10' name='groups' syntax='string' mapName='groups' mapType='string'/>2) Is the groups attribute already a list? If not (e.g. no groups yet assigned), the append statement might not actually do anything.
3) Your statement below the append doesn't actually do anything. Well, it should not break anything, but who knows.