I had one of my meeting reminders that just would not go away, causing my iPhone to quickly run out of batterie... I tried to go in the webmail server and remove that meeting and no luck, it keep coming back... Here what my IT dep told me to do and it did fix the issue:
The easiest way to try to get rid of corrupt reminders is by closing Outlook and reopening it using the /cleanreminders switch. To do this, press Windows key + R to open the Run dialog. Then type: outlook /cleanreminders in the field and press Ok. Make sure there is a space between outlook and the /