We have 2007 Microsoft Outlook Exchange and we have 1 user who is having a problem with his calendar. When he tries to open his calendar it comes up with the error, The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action. He is online and he is not having a problem getting his email or sending emails, it just seems to be his calendar. He can access it through webmail but the issue only seems to be in Outlook. I right clicked on the calendar and then clicked on open in a new window and then it finally opened. What could be causing this? Nobody else is having this issue and like I said, any help would be greatly appreciated.

See if he has the problem with a different profile.  Then see if he has the problem on a different computer.  If the issue follows him to a different computer, then you might consider creating another mailbox.  If it doesn't, you might have a problem with Outlook or the profile.