Hi Refayi,
This is caused by incorrect time or time zone settings on one of the computer.
1. Verify all computers involved are set to the correct time, time zone and daylight savings time settings in Windows Control Panel's Date and Time applet.
2. Verify the settings are also correct in Outlook.
Tools -> options ->Preferences tab Calendar Options button -> Time Zone button
If you are using Outlook 2010 you need to use a time zone with the correct DST settings for your location. If your location does not observe DST, do not choose a time zone that does then deselect the option to automatically update for daylight saving time.
You need to use a time zone that does not observe DST.
In Outlook 2007 and Outlook 2010, if you receive an iCalendar that does not include time zone offsets in the ical, Outlook may place the appointment on your calendar using standard time, not current time. For example, if you subscribe to an Internet calendar
that does not include DST information, Outlook will treat the events as referencing standard time and move them ahead an hour if they occur when DST is in effect. As a result, an appointment scheduled for noon will be on the calendar at 1 PM.