>>Over the weekend I installed DOTLESS package into my ASP.NET Web Forms project. And I was testing the application without problems.
>>
>>But today when I try to run/debug the project (without any major changes) I get the following error:
>>
>>

>>0x800a139e - Microsoft JScript runtime error: ASP.NET Ajax client-side framework failed to load.
>>

>>
>>The error is called by the following code:
>>
>>

>><script src="/bundles/MsAjaxJs?v=J4joXQqg80Lks57qbGfUAfRLic3bXKGafmR6wE4CFtc1" type="text/javascript"></script>
>><script type="text/javascript">
>>//<![CDATA[
>>if (typeof(Sys) === 'undefined') throw new Error('ASP.NET Ajax client-side framework failed to load.');
>>//]]>
>>

>>
>>Any suggestions to what causes and how to fix this issue?
>>
>>UPDATE: some additional information. When I start/debug the project in Chrome, no problem. So the problem is only when I use IE (9.0).
>
>Hmm. Seems to me there are two possible causes:
>(a) Browser doesn't find the script at the advertised URL or
>(b) The JavaScript test to determine whether it was loaded OK isn't valid (or runs too soon)
>
>Use the debugger in Chrome to check (on the Network tab) whether the script is downloaded OK.
>If it is then do the same in IE. If it downloads OK in IE then check when the 'if(typeof(Sys).....) runs.
>
>Oh, and make sure that Chrome doesn't just *appear* to be working because the script has been cached.......

I believe your suggestion was the most helpful. I do find that in Chrome the scripts load fine. But in IE no. I have Googled and I found this problem discussed since 2008 and there are thousands of solutions; each a different one. Basically I write it off as MS IE crap.
I will stop debugging and testing in IE for now. One would think that MS when designing VS would make it work flawlessly on IE but not so.
Thank you.