Error not displayed after AGS call

We have a custom form that is calling out to a modified version of HR11. When a BSI tax factory error is detected a message should be displayed indicating that tax errors exist and the user can click off to continue. At some point either through upgrading to LSF 9, upgrading to BSI or modifying the custom DS form, the error has stopped being displayed. The code to check for errors after the AGS call is as follows. Any ideas on where to start with debugging where this is broken?

AGS CALL OCCURS HERE

if (!sAGSInfo || sAGSInfo.status > 400)
  alert("Got 400 error");
   return;

  var sMessage = sAGSInfo.selectSingleNode("//Message").text;

  if (sMessage != "Update Complete - Continue") {
   alert (sMessage);
   alert("Got other error");
  } else {
   // set hiring status message
   lawForm.setFormValue("hire_status","Update Complete - Continue");
   alert("Applicant data has been updated");
  }