Cannot address user - is in Directory and views, but not in type-ahead

HiWe have 2.600 users and 1 cannot be addressed by type-ahead. The user has the same name as another user but with different /OU. The user has a unique shortname and appears correctly in all view I have checked ($Users, $Vim… ect.)

In a new Memo I can find the user by selecting her in the dialog, and the name appears correctly in the To field, but pressing F9 gives me “The name is not in a directory”. When adressing directly in a mail by full name or shortname I get “The name is not in a directory”.

Sending the mail to shortname or full name anyway delivers the mail correctly to the users mailbox.

What on earth is going on?

I have tried downing the server and running fixup and Compact -c but no luck.