We are having an issue with LDAP authentication and user administration that is becoming a Serious and Urgent one to resolve.

The Scenario:
The Business Space (application) is hosting a business application used by a large user group within a global mining company. We are using Single Sign-on through LDAP authentication.
The AwareIM application is configured in such a way that we (an Administrator) add users manually to RegularUsers and link this user to the relevant LDAP user through the sAMAccountName attribute.
AwareIM stores the LDAP_DistinguishedName attribute for the relevant user in the LDAP Object table.

Problem Statement:
The LDAP is maintained by a Global Service provider for the client and we don't have full visibility on when and what changes are made to the LDAP configuration.
As soon as the LDAP entry for ONE of the users that has been added to the AwareIM application change in any of the following ways:

1. The DistinguishedName attribute is changed in the LDAP; or
1. The user account is removed from the LDAP.

Then all the users previously configured to have access to the AwareIM application are unable to login to the application.
The Wrapper.log file has an Error that looks like this:

jvm 1 | 2011/02/28 13:05:32 | 2011-02-28 13:05:32,219 ERROR -Unable to login due to system error
INFO | jvm 1 | 2011/02/28 13:05:32 | com.bas.basserver.executionengine.ExecutionException: Internal error. Problem in sAMAccountName.displayName for shortcut attribute SC_LDAP_User Error reading LDAP entry CN=Houghton\, Yvette (Manganese - BI Contractor),OU=Contractors,OU=Manganese 6 Hollard,OU=Users,OU=Corp Johannesburg,OU=Corporate,DC=emea,DC=ent,DC=bhpbilliton,DC=net No Such Object
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.executionengine.s.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.executionengine.s.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.executionengine.ExecutionEngine.doExecuteQuery(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.executionengine.ExecutionEngine.executeQuery(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.session.SessionManager.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.session.SessionManager.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.session.SessionManager.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.session.SessionManager.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.session.SessionManager.login(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.channels.ChannelManager.handleSocketLoginRequest(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.bsmanager.k.run(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at java.lang.Thread.run(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | com.bas.basserver.executionengine.ExecutionException: Internal error. Problem in sAMAccountName.displayName for shortcut attribute SC_LDAP_User Error reading LDAP entry CN=Houghton\, Yvette (Manganese - BI Contractor),OU=Contractors,OU=Manganese 6 Hollard,OU=Users,OU=Corp Johannesburg,OU=Corporate,DC=emea,DC=ent,DC=bhpbilliton,DC=net No Such Object
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.executionengine.s.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.executionengine.s.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.executionengine.ExecutionEngine.doExecuteQuery(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.executionengine.ExecutionEngine.executeQuery(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.session.SessionManager.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.session.SessionManager.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.session.SessionManager.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.session.SessionManager.a(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.session.SessionManager.login(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.channels.ChannelManager.handleSocketLoginRequest(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at com.bas.basserver.bsmanager.k.run(Unknown Source)
INFO | jvm 1 | 2011/02/28 13:05:32 | at java.lang.Thread.run(Unknown Source)

Interim Solution:
We have to find the user account that causes the problem and either correct the LDAP_DistinguishedName field in the LDAP table or delete the user and re-create the user account for the AwareIM application. (We only have to delete the entry in the RegularUser Objects to get the remaining users to be able to log on.)

Question:

1. Why does a single user entry in the RegularUser table that is linked to a invalid/non-existent LDAP account cause all the user logon attempts to result in exception and therefore they can't access the appellation?
1. Is there another/better way to configure the login option or user objects to solve this problem?