Secret mismatch


An Elastix 1.6-14 serving Aastra IP Office 4222 (version 1 & 2).
When I set the secret parameter for an extension, The extension can not make calls, only receive them.
When I leave the secret parameter out , everything works fine.
(Off course I set the extension password in the config of the extension according to the secret set in Elastix)

How can I make the extension use the secret?

I made a wireshark trace of a client<>server communication containing the initial invite of the friend , the authentication required from the server and the ACK response from the friend.

Where in this conversation should the secret (password shared by server/friend) parameter be found?