Try these steps...
Resetting iSync data
Sometimes it is necessary to reset the sync data on your computer(s) and on your .Mac account. For example, if your .Mac syncing begins to behave oddly or information isn't synchronizing correctly then resetting the sync data is a good troubleshooting step. It's also sometimes a good idea to reset the sync data after Chronos releases updates to their software that have made improvements or enhancements to synchronization.
If you don't use .Mac and you only need to reset the sync data on a single computer, then perform the following steps:
1. Launch the iSync application: /Applications/iSync
2. Choose iSync > Preferences.
3. Click 'Reset Sync History' button. You'll be asked to confirm the selection. Choose 'Reset Sync History' to confirm.
4. The iCal application may launch at this point (feel free to quit it). Synchronization will automatically start to take place in the background and may take a while depending upon how much data you have to synchronize. It's also not uncommon for the several processes involved with synchronization to use quite a bit of CPU during this process.
If you use .Mac and you need to reset the sync data on multiple computers and your .Mac account, then perform the following steps:
FIRST: RESET SYNC HISTORY ON EACH MACHINE
1) Launch the iSync application: /Applications/iSync
2) Choose iSync > Preferences
3) Click 'Reset Sync History' button. You'll be asked to confirm the selection. Choose 'Reset Sync History' to confirm
4) Repeat these steps on each computer
SECOND: SYNC YOUR FIRST COMPUTER TO .MAC
1) Move to your first computer. This should be your machine that has your correct contacts, calendars, and notes data
2) Open the .Mac System Preference Pane
3) Click the Advanced tab
4) Click the Reset Sync Data button.
5) From the Replace pop-up menu, choose the information you want to reset, such as Contacts, Notes, or all data.
6) Choose the option to replace All Sync Info on .Mac with sync info from this computer
7) Click Replace. This will copy the information from your computer to your .Mac account, replacing the information on .Mac with the information from your computer.
THIRD: SYNC YOUR OTHER COMPUTERS WITH .MAC
1) Move to your next computer
2) Open the .Mac System Preference Pane
3) Click the Sync tab
4) Click the Sync Now button. Your computer will begin to synchronize with .Mac. You may be asked if you would like to merge or replace certain kinds of data. Unless you have a good reason to merge, you should choose the replace option which ensures that the latest data on .Mac overwrites the data on your computer.
At this point, all your computers should be synchronized.
