Thanks for posting this Lego Pirate. This happens to me all the time, and without any need to open multiple tabs (I am using Firefox 3.6.8) or anything like that.
It appears to be time-out related. If I let any tab or window with the Chat-Move-Notes tab hang around for too long, and then try to post a Note to myself in the Notes tab, I get this popup, and lose any ability to save my Notes.
For me, this is the most annoying thing about this otherwise excellent site, since I tend to use Notes a lot.
I don't know why I still fall for it - I've got to remember to hit Refresh in the browser before even thinking about posting a Note.
I'm sure this is related to the well known (to me) bug that you can make a move and hit Submit only to find the whole thing get reset when the HTTP post is executed - because you've timed out.
I keep getting an alert from chess.com: "An error occurred during AJAX Response parsing. The error response will appear in a new popup."
This is very reproducible with the latest Safari and OS X. A typical scenario occurs in my preferred method of interaction with the games:
The workaround is to remember to refresh the game window after copying the notes, then paste the notes into the refreshed window, but it is easy to forget this and bingo, notes gone.
Can something be done about this?