A co-worker brought me her HTC Aria to help with an OS upgrade to Froyo. I did the OS upgrade and it seemed to go fine. The next day she returned with her phone displaying the error: Client/Server Conversion Error on her Exchange Calendar only. Her email and contacts were fine.

To repair this error:

• Open your Settings
• Open Accounts and Sync
• Tap the Exchange account you are having issues with (some people *me* have more than one Exchange account set up)
• At the bottom tap Remove Account
• Return to Settings
• Tap Applications
• Tap Manage Applications
• Tap All at the top
• Find Calendar and Tap on it
• Tap Clear Data
• Go back one screen and find Calendar Storage and Tap on it
• Tap Clear Data

Now remove your batter to reboot your phone. Rebooting may not be necessary but it certainly won’t hurt.

Once the phone has rebooted, add your Exchange account again and set up your sync. The error should be gone now.