I have a user with a very similar problem. If she composes a new mail message then the GAL is displayed with no problems. If however, she wants to send an attachment and then goes to a folder view, selects the file for attaching, then right clicks and chooses 'send to email recipient'. This opens up a balnk email and if she clicks on the 'To' button she doesn't get the GAL displayed. I have given her a work around which is to create the email first, then browse to the folder and drage and drop the attachment into the email.
This works, but obviously, I'd like to know why Outlook is behaving in this manner.
I have checked the usual suspects in this - Tools, Options menu, GAL is the default address list (as confirmed by the fact that Outlook is only doing it for this one user and that it IS displayed under all circumstances with the exception of the attachment method).
Thanks for any light anyone can shed on this annoying little feature.