Cannot open additional "secondary" mailbox

I have a user that has the VP's mailbox configured in her Outlook as a "additional" mailbox, so she can assist him in scheduling mettings, etc..
A few days ago, the "additional" mailbox stopped opening. The user can still acces her own email as normal.
When you click on the "additional" mailbox in the right pane, a window pops up saying, "trying to recieve data from "server-name".
Following that is an error message saying that it could not open "such and such mailbox from such and such server".
Possible reasons:
 - .pst or .ost is unavailable.
 - .pst or .ost is protected by permissions.
 - .pst or .ost is on a share or server that is unavailable.
 - .pst or .ost is corrupt.

What I have checked:
 - User has internet connectivity.
 - User can ping gateway, dhcp, dns servers.
 - The .pst is not corrupt
 - The .pst is not protected by permissions.
 - The .pst is on an available server.
 -  Ping times out when trying to hit the exchange server. (but she can still recieve her own email)
 - Tracert bombs out when trying to hit the exchange server. (" " ")
 
On my laptop, I can ping, tracert, nslookup, etc.. to the server successfully.
The server is definitely up.

I setup her email account on a spare laptop, and added the VP's mailbox as an additional mailbox, and it works fine. So, that leads me to believe that the problem is my users laptop.

What can I do to fix this issue?

Thanks in advance.