This is another LC throttling maneuver.
A few months ago LC began returning an error rather than the browsenotes file for requests more closely spaced than 30 seconds.
Starting a few days ago a different error message (making reference to the new URL) is returned for requests more closely spaced than 2 minutes.
Note that if a download attempt is made and error returned, the timer resets to the full 2 minutes.
Yes Anil, "The times they are a changin"