Vista - MS exchange server issues over VPN line

Guys
I've took it upon myself to hopefully get this isssue resolved.
Pls I require your technical assistance.

Scenario: User is working from home connected via VPN, he is unable to gain a connection to his msx svr.
Error: Cannot open your default e-mail folders. You must connect to Microsoft Exchange with the current profile before you can synchronize your folders with your offline folder file.
I'm able to resolve his name via profile settings indicating authentication with msx svr has been granted.
Default gateway is present, msx svr can be seen by client through ping cmd

Found article under Error messages when you try to connect Outlook 2007 to Exchange Server: "The action cannot be completed" or "Your Microsoft Exchange Server is unavailable" or "Cannot start Microsoft Office Outlook"
1. Click Start, click Run, type regedit in the Open box, and then click OK.
2. Locate and then click the following subkey:
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\RPC
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type DefConnectOpts, and then press ENTER.
5. Right-click DefConnectOpts, and then click Modify.
6. In the Value data box, type 0, and then click OK.
7. Exit Registry Editor.
This worked for the first time, then the next day the problem returned.
I expect after further deployment of Vista a lot more home-workers will experience this problem.

Your help will be most appreciated.
Kind regards
Paul -Vista pilot support analyst

Guys, the problem seemed to be with the Network and sharing Center
Select Network and Sharing Center > Change the users network to private via the ‘Customize’ option
Disconnect\reconnect to VPN

NB: The Private or Work network location options allow file & printer sharing and Network discovery (other users can see you). A Public location doesn't allow any of these features.

Also this will explain the irregularity of this problem as not all users would be affected.

I hope somone finds this information useful.