The problem is probably caused by this breaking change in .Net 4.0
. I am guessing that you are using RadCompression or some other module that interferes. As explained in the article you should set the preCondition to "managedHandler" for the module. Note that you may also need to remove the following setting from your web.config which might have been added automatically:
As explained in this article
, this setting essentially negates any preConditions you may have set and forces all modules to run for all requests which results in erroneous behavior. If you remove it, the module will be correctly excluded from the request and the events should be executed.
Let me know if this helps or if your problem is different.
the Telerik team