Chances are that you have a mismatch between Windows' DST setting and
Outlook Calendar's DST setting. First check WIndows by double-clicking on
the clock in your System Tray, choosing the Time Zone tabe, and making sure
the checkbox at the bottom is selected, if appropriate to your time zone.
Click OK. Then check Outlook's setting by clicking Tools>Options>Calendar
Options>Time Zone and making sure the "Adjust for daylight saving time" box
matches the Windows settnig you checked above.