This problem could be both client/server-side error, I think it may seem to be both in your case.
Have you changed your chat name recently lower-case letter was changed to upper-case?
Maybe the server back then couldn't recognize that slight change in the URL, because it seems that from the way the problem was solved that the error has occurred when you typed Frtka the "f" with uppercase, it's imperative to make sure that the URL is typed all correctly. Without any further ado, if this error happens again you can try refreshing the page multiple times to get the right connection between the Web-Server and your web browser also try to clear cache/cookies when it happens again.
Note that I can access the chat right now even if I changed the letters case, you also may have been able to access it like me.