This question is actually the answer to a question like "why does MicrosoftMvcAjax.js throw an unknown runtime error in IE8 or older".
I have not been able to find/google any discussion or other answers specific to this question, or a fix for it apart from what is in the linked question.
I wonder if someone (a mod?) can;
- Re-open this question (to stop it from possibly being deleted by a clean-up) and;
- Convert it into the correct question/answer format
It would be a shame to lose this excellent fix due to the author's formatting