The error is "webresource.axd and scriptresource.axd 404 not found" whenever I do any async call I use to get this error "sys is not defined". I have tried a lot to fix this issue by following the below links.
and so on ....
After spending 4 hours I found a new property on asp.net 4.0 called EnableCdn that basically, if it's set to "true", it loads the resources from the Microsoft content resource servers.
Refer this link for information about EnableCDN.
This worked like a charm and fixed my issue.
I hope this snippet can help many techies. :-)