The user search fails when Redirect schema is enabled in Admin console LDAP configuration screen, it was working fine in 9.1SP1 but upgrade to SP5 breaks it.
Strong Authentication
Risk Authentication
Release: 9.1SP5
This is a regression issue in the product and Advanced Authentication team has provided a patch to address this issue. The patch is uploaded to this KB article for download as well. Upgrade to 9.1.5.1 version addresses the issue as well.