You can try using the /cleanreminders command line switch as described he
http://www.outlook-tips.net/beginner/switches.htm

"Daniel Mazur" wrote in message
...
I have recently transferred PST Outlook account to our Exchange 2003 Mail
server, all mail, tasks, calendar and other data. Everything went fine,
except that all my task reminders are gone. Is there a way to reactivate
the reminders? I have been searching for an answer but to no avail.