Calendar duplications

Hi,
Client has Outlook 2007, Google Calendar and smart phone, all syncing to the Google Calendar. Problem is old deleted events and reminders keep showing up in Outlook even though they do not appear on Google Calendar. Recently, after not being to resolve the issue, I removed the Google Calendar Add-In from Outlook so that Outlook would not sync anymore, and these old items are still reappearing!
Example: Within hours of removing the Outlook Add-In, Google Calendar reported that it was deleting 19 items. Client clicked OK on the message, and immediately 19 reminders for the old events popped up in Outlook. What? Computer was rebooted after removing Add-In.

From what I am reading this issue has been around for years, and some people never find a solution in their individual cases. I want some feedback from anyone that has felt with this issue if I am understanding this correctly, and, if you found a solution that worked for you, what was it?

Thanks,
Bill