Though there are some admins that hang around in this XPages forum that might be able to help..

It could be that the server is unable to resolve the name to a Person doc.

Have a look in the DA config, on the LDAP tab.  Have you filled in the field "Attribute to be used as Notes disguished name" with the AD field you are using to hold the Domino Notes Name?

For example:

In my test domain I am using the Office AD field to store the Notes Name

Office: CN=Test User,O=DEV

Then in the DA config I have

Attribute to be used as Notes disguished name: physicalDeliveryOfficeName

Thanks for the suggestions, unfortunately the admin is on holiday for a week, so once he's back, I'll get him to take a look and feedback.

Thanks