PrincipalContext.ValidateCredentials always returning false


I have an application which uses DirectoryServices to validate an active directory username and password.  Up until the other day, it worked fine.  Now, the ValidateCredentials function of System.DirectoryServices.AccountManagement.PrincipalContext always returns false.  The application hasn't changed.  I don't believe there have been any infrastructure changes, except that the network did have a windows Certificate Authority which expired over the weekend.  Could this be the cause?  The network admins don't think the CA is tied to Active Directory authentication, but I don't know of anything else that has changed.  It is a Win2k8 R2 Domain.  Any ideas?  Thanks
Martin BertramAsked:
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You can take a look at this page :

In short, make sure userPrincipalName is the same as the account name and msDS-UserAccountDisabled is set to false.

Can you confirm that one account you are testing with has those two field correct as per the article ?

Just to eliminate a probable culprit.

Thanks !
Martin BertramAuthor Commented:
Thanks SylvainDrapeau.  Checked that out and it wasn't it.  Also this did work for many months up until a few days ago.
Martin BertramAuthor Commented:
It turns out this was being caused by our expired CA that was integrated with Active Directory.  After the network admins fixed the CA issue, the function worked normally again.

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Martin BertramAuthor Commented:
Found that the issue was related to a Certificate Authority installed in the network which had expired.
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