Outlook Calendar Time Issue

[WildKat]

I am having an issue when I create a meeting at a certain time and add invitees, the time on their calendar is off by 2hrs. It doesnt happen all the time and it only happens to a select few. I have checked the time zone settings both in Outlook and in Windows in all machines concerned and everything is set to GMT.

Can anyone suggest any further troubleshooting?

Many Thanks

(Exchange 2003 / Outlook 2003)