Something's interfering with Outlook's connection to your mail server (obviously). Here are some tips from Microsoft itself:
• There are corrupted files on your hard disk.
• You are running Norton Personal Firewall 2002.
• You are running Norton Internet Security software.
• You have installed an update to Microsoft Office.
• The Norton anti-spam add-in is enabled in Outlook.
Note Norton Personal Firewall 2002, Norton Internet Security software, and the Norton Anti-Spam add-in are supported by Symantec Inc.