Google reports that a small number of their mail users are experiencing problems accessing messages in the late morning of Tuesday April 17. This affects both GMail and Google Apps (Macalester's version of the tool). Google staff are aware of the problem and are actively working to resolve it. You can check their progress on the Google Apps Status Dashboard, if desired.
Update, 1:25 PM: Google reports that the problem has been fixed. If you are still having difficulty accessing your mail, try clearing your browser's cache and restarting it. For assistance, please call the ITS Help Desk at 651-696-6525.