FINALLY!
This error has been showing up in my server error logs for over a year now. There are literally thousands of errors reported. Typically, for whatever reason, when it is reported it is reported dozens of times at once from the same TD. The server actually limits how many errors can be reported to prevent overwhelming the server, so after 20 or so errors reported the server essentially "bans" the endpoint and just ignores it. I had to do this because I released a version a few years ago that reported an error every time the main screen was updated (once per second) but didn't show any error to the user. Some people left the TD running for days so there were tens of thousands of errors reported.
Anyway, this error has been driving me nuts because I have NEVER encountered it myself, but I have done everything I can to figure out what's wrong. But I just don't see this error. Ever. And after a year you are the first person to ever report it!
It's a little strange because it isn't the TD error dialog, it's the built-in IE error dialog, which shouldn't happen. But that gives me a little bit of a hint as to where it might be occurring.
Alright, so when do you see it? Does it happen at some point consistently?