These instructions are probably overkill but I wanted to cover all bases.
1. Fire up your Mac and connect the iPad.
2. Open iTunes and confirm that you are NOT syncing the calendar via the cable. Change settings as appropriate. When finished, disconnect the iPad and power it down.
3. Open iCal on the Mac and confirm that the events are correct. Add/delete events as appropriate. Quit from iCal.
4. Open System Preferences > MobileMe > Sync
5. Click on "Advanced" and then click on your Mac when it shows up.
6. Click on "Reset Sync Data"
7. At the top, Replace: Calendars
8. Click the right-pointing arrow so that the complete text states: "Replace Calendars on MobileMe with sync info from this computer."
9. Click "Replace"
10. You've confirmed that your Mac and MobileMe are set up properly. Now, fire up the iPad and go to Settings > Mail, Contacts, Calendars.
11. REMOVE Calendar syncing from the account that's identified by your email address.
12. Follow the instructions below.
http://docs.info.apple.com/article.html?path=MobileMe/Help/en/mmcc733205.html