Do you have 2 copies of the appointment?
Seehttp://
www.slipstick.com/calendar/cleanreminder.aspfor methods
that may work since cleanreminders didn't.
'Outlook & Exchange Solutions Center' (
http://www.slipstick.com)
'Outlook Tips' (
http://www.outlook-tips.net/)
I found that on a new installation of Outlook 2010 i had two reminders
and two to-do's for every task. Somehow it created two listing for
the same outlook data file in file / info / account setting / data
files / tab. The same outlook PST was listed twice.
Exit Outlook and make a backup of your PST file in case something goes
wrong.
Go back into outlook data file in file / info / account setting /
data files / tab. Remove the one that is not the default with the
same name and location. Close this and go back to outlook. Weird
stuff happens - things disappear - don't panic yet. Close outlook.
Reopen outlook. My installation was fixed.
I'm posting this because this drove me nuts for two days and I didn't
want someone else driven nuts by this.