I have used this solution (disable reminders) to 'band aid' another issue;
About 476 reminders (all contacts) pop up and cannot be removed from the
reminder list. I tried dismissing single reminders, all reminders, opening
individual contacts and clearing flags/reminders, marked them 'completed',
all to no avail. This issue was in the 2007 pst file, so I brought the
problem along when I imported into ost/exchange. The contacts may have been
sync'd with a PDA in the past and with outlook 2003. Calendar items are not
an issue.
Running scanpst or scanost have not worked.