Calendar not syncing iPhone 4

Dear All,
Recently I found out that my iPhone Calendar is not syncing with my MobileMe. I deleted all contents in the MobileMe through my Mac and re-synced and nothing showed on my phone. I deleted the account on the phone then re-installed it same everything got synced except the calendar.
What could be the problem and how can it be solved?
Thanks
Debbeh
MacBook 15" (Mid 2009) Mac OS X (10.6.4) Powerbook 1 Ghz 12,", MacBook 13" (Late 2008), iPhone 2G, 3GS, 4, iOS4.1