Problems adding Microsoft Exchange Account to Outlook 2007

I am trying to add a Microsoft Exchange account to my desktop that is running Windows 7 and Outlook 2007.  Currently I access this account via OWA.

After entering the "Microsoft Exchange server" and "User Name" ("Use Cached Exchange Mode" is checked) I receive this error message "The action cannot be completed.  The connection to Microsoft Exchange is unavailable.  Outlook must be online or connected to complete this action."

I have successfully connected this account to my laptop (running Windows 7 & Outlook 2010) following the same steps so I'm unsure why I'm having issues on my desktop.

Any help would be appreciated.