Report ID: 1235425033 (first-time sync)
I just tried to sync my library for the first time (about 4300 entries -- I'd been backing it up locally but decided to try online sync so it would be available on other computers too), and I got this error. It appears to have backed up all of my library successfully. But the little exclamation point error appeared and it claimed it hadn't been backed up yet. I tried syncing again (this it me much faster) and it worked. So I'm just reporting this in case it's useful to developers.
Report ID: 1235425033
Message:
Report ID: 1235425033
Message:
[JavaScript Error: "obj.toJSON is not a function" {file: "chrome://zotero/content/xpcom/sync/syncEngine.js" line: 1448}]