This is from the analysis board for my current game with Rattusrex.  I was in the notes tab of the analysis board and had begun making some moves.

I'm using Firefox v.2.0.0.9

Here's the link for the game from which I opened the analysis board:
http://www.chess.com/echess/game.html?id=967021

From the analysis board, there was a message at the top "Firefox prevented this site from opening a pop-up window".
My current status is 'on vacation'.

I'm not sure if this is common or not.  It's never caused an error that I can recall and to be honest, I don't always notice these messages.  Wanted to include this information as it may be helpful in root cause analysis.

Here's what happened:
1.  Got error message.  Sorry, didn't recall what it said in detail, but believe it had something to do with AJAX.  I clicked 'Ok' button

2.  Another error message popped up.  Title of error message was 'The page at http://www.chess.com says:'

Error message was: objErrorWindow has no properties on line number 152 in file http://www.chess.com/assets/js/_core/post.js

3. Clicked ok button, another error message resulted with same title.

Error message was:  An error occurred during AJAX Response handling.  The error response will appear in a new popup.

4.Clicked OK button.  error window closed but in analysis window, to the left of the Notes tab, a circular progress image appears rotating in counter-clockwise direction.

 

Game ran fine after that.  Hope this helps. 

can you reproduce this error? or was it a one-time?

It's happened a couple of times, but I cannot reproduce it.  Was hoping you may have some error log messages that corresponded to the time.  Having worked in the IT industry, I added all the information I could that may be helpful in identifying the root cause.  Let me know if there are any other bits of info I missed.

 

If I see it again, I'll try to report again.