Sending vCard – “You can’t send a message on behalf of this user unless you have permission to do so … ” – Outlook 2010
If you run into this message while trying to forward a vCard using Outlook 2010 (likely 2007 as well), you are dealing with a hidden x400 "FROM" address inside the contact metadata. When a contact is created, outlook will cache the "from" address and reference it instead of the actual account being used to send. You will see this when contacts are imported and exported between exchange services, and apparently POP3 as well.
Sadly, there are only 2 resolutions and neither of them are global.
1) When you see the “FROM” field appear while forwarding a contact, manually click "From" -> "other e-mail address" -> and choose your name from the list.
This will change the “from” address to your correct address, hit send, and life is good.
2) You can manually create new contacts and copy the information from the old to the new.
DO NOT right click and copy a contact, you need to make a new contact and copy each field over individually.
If you copy a contact, it will transfer the x400 metadata.
I strongly feel this is a bug and Microsoft should look at removing the reference to the old address.