I'm having a really tough time getting the Global Address List from our Exchange 2007 server to download on some Windows 7 64bit Professional laptops which have Office 2010 32-bit installed. The laptops are configured with Cached mode and RPC over HTTPs (Outlook Anywhere) because it makes good sense for a laptop to be configured this way (can still read e-mail with a slow wifi or no connection).
The GAL works fine on a system that is hardwired into the network without Cached mode enabled, and a direct connection to Exchange (no Outlook Anywhere setup). In fact on these laptops the GAL works fine the first time the Outlook profile is setup. Once you close outlook and restart it after the mailbox is fully sync'd, the GAL is gone. Another side effect is when replying to email that goes outside of the organization. Sometimes Outlook will create a pop up dialog that says "The operation failed. The messaging interfaces have returned an unknown error. If the problem persists, restart Outlook. Cannot resolve recipient." I had this issue and I ended up having to save it as a draft, then logging into OWA and noticed it was saved with SMTP= in front of each address. I was able to remove that and send the email through OWA in Internet Explorer just fine. In Outlook 2010 it can send email fine internally and to anyone external that is already in my personal contact list.
I'm not really sure what the problem is here, but it seems isolated to Outlook 2010 clients with Cached mode and RPC over HTTPs.