Have you looked in the logs to if there is any sync errors? Also what version of Outlook and What version of AS are you using. I've seen errors syncing certain items (Contacts but not calendar for example) when there are errors in the PST file on the PC [that can be usually be fixed by running ScanPST on your PC] or corruptions in the PIM.vol file on the Phone (backup your PIM data with dotfreds PIMbackup utility, delete the PIM.vol and let the system create a new one)...
There's a couple of ideas.
Mark

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