We downloaded the 4.1 control and overwrote with the new DLLs.  Not sure how the old 4.0 source code could have been modified.  Do you distribute source code?   We still have the same situation.  I have also tested uploading the new 4.1 LiveSupport without any modificaiton including images and can produce the same exact error.  Is it possible a class is not being set corectly from the remote domain scrpts?