I upgraded to an iPhone 4S yesterday and have been playing with one of the new features, Siri, trying to get it to understand “Text my girlfriend”. I had associated Emma with my contact record but it wasn’t finding her contact record in the address book.
I store most contact records as Title, Firstname, Surname. E.g.:
Miss Jane Smith
Mr John Doe
If you ask Siri to make an association then in your contact record it will store the name of the relationsip (sister, brother, etc) and the full name including the title.
However when it tries to lookup that relationship it will fail.
The simple fix is to remove the title from the relationship on your contact record and it should all start working again.