A potentially dangerous Request.Path value was detected from the client (*)

If you're using .NET 4.0 you should be able to allow these urls via the web.config

<system.web>
    <httpRuntime
            requestPathInvalidCharacters="&lt;,&gt;,%,&amp;,:,\,?" />
</system.web>
Note, I've just removed the asterisk (*), the original default string is:

<httpRuntime
          requestPathInvalidCharacters="&lt;,&gt;,*,%,&amp;,:,\,?" />