ajax file extention allow and wrong file .axd redirect on error page

<configuration>
<system.web>
    <trace enabled="false"/>
<pages viewStateEncryptionMode="Always" enableViewStateMac="false"></pages>
<compilation debug="true" targetFramework="4.0"/>
<customErrors mode="On" defaultRedirect="~/error.html">
<error statusCode="403" redirect="~/error.html"/>
<error statusCode="404" redirect="~/error.html"/>
<error statusCode="500" redirect="~/error.html"/>
</customErrors>
    <httpRuntime enableVersionHeader="false"/>
    <!--Below Added to secure cookie-->
    <httpCookies httpOnlyCookies="true" requireSSL="false"/>
    <!--Above Added to secure cookie-->
</system.web>
  <system.webServer>
  <!--The following configuration sample adds an HTTP "Cache-Control: no-cache" header to the response, thereby disabling caching of requests.-->
  <staticContent>
    <clientCache cacheControlMode="DisableCache" />
  </staticContent>
  <!--Above Added to HTTP "Cache-Control: no-cache" header to the response, thereby disabling caching of requests.-->
  </system.webServer>
<system.net>
<mailSettings>
<smtp>
<network host="localhost"/>
</smtp>
</mailSettings>
</system.net>
</configuration>