Hello,
I don't believe this is being caused by Kentico, since iit looks like the exception is from an external source. Unfortunantely, it is pretty hard to say what could be causing this issue. There are lot of discussions on the internet regarding this issue and many of them have completely different solutions.
Could you please try to read following article for a possible explanation?
LinkAre you using some 3rd party control for example like telerik which could cause this issue?
http://www.telerik.com/community/forums/aspnet-ajax/ajax/quot-this-is-an-invalid-webresource-request-quot-exception.aspxhttp://stackoverflow.com/questions/2184197/this-is-an-invalid-webresource-request-javascript-datetimepickerThis does not look like a big issue and you could stop logging such a harmless exception in the ~\App_Code\Global.asax.cs file in LogLastApplicationError method, similar as it is described in following article:
www.telerik.com/community/forums/aspnet/spell/this-is-an-invalid-webresource-request.aspx
If you need help with anything else, please let me know.
Regards,
Edward Hillard