I keep getting hundreds of these "Could not synchronize record: […]" errors, but the meetings and emails refered to in the Errors panel do not exist – I deleted them, and confirmed that they are not in any folder, calendar, or anywhere.
They say error number: 19759
E.g.:
Best Answer
It turns out that these meetings were still on the hard drive. I went to Finder, searched on the title of the meetings (which was in the Error message itself), and simply deleted the files in question. They were kind of "grayed out", which led me to believe they were either owned by another user or had failed to get deleted correctly.