IIS Error : Could not load file or assembly 'System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

Error

Some times we face Application error in "/" application after migration the ASP.net site from one server to other ever after making all the changes perfect.

Error :  Could not load file or assembly 'System.Web.Extensions,

Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of
its dependencies. The system cannot find the file specified.

Resolution:

1. Check if you application folder contains a folder with name "ajax" when you copied it from old server.

2. If yes then download and install the Ajax Extensions 1.0 for ASP.NET 2.0 on new server.

3. Reset the IIS (though it is not necessary but its good to reset IIS after such installation.)

You can download Ajax Extensions 1.0 from from Microsoft Download Center.

Solution Applies to:

Windows Server 2003. IIS 6.0, ASP.Net 2.0

How To Check If Trace\Track is Enabled on an IIS server

What is Trace \ Track on IIS

Trace \ Track is a vulnerability that is usually identified on an IIS server when we run PCI compliance and find this vulnerability. A hacker can run a Trace attack on IIS Website and get information about the Backend server and other important information.

In latest versions on IIS (IIS 6.0, 7.5) Trace is disabled by default but still it is good idea to make sure that Trace is disabled on IIS.

Testing if Trace \ Track is Enabled on a IIS website or not

Follow these steps :

1. Go to command Prompt of your Machine.
2. Type telnet <URL of the website> 80 (this will open a telnet session of that website on port 80)
3. Type following commands on the telnet session screen in exact same order: 

      TRACE / HTTP/1.0
    Host: <hostname_you_are_testing>
    TestA: Hello
    TestB: World

4. Press enter twice. 

If Trace is enabled on your server, you should see following results:

      HTTP/1.1 200 OK
    Server: Microsoft-IIS/5.0
    Date: Tue, 04 Aug 2009 20:17:15 GMT
    Content-Type: message/http
    Content-Length: 76 

And If you receive following results on the telnet screen, then Trace is enabled :

     HTTP/1.1 501 Not Implemented
    Content-Type: text/html
    Server: Microsoft-IIS/7.5
    X-Powered-By: ASP.NET
    Date: Tue, 15 Oct 2013 12:21:33 GMT
    Content-Length: 1508

    Connection: close


Disabling Trace or Track on IIS

The easiest way to mitigate the risk of Trace \ Track on iis is  : installing URLScan from Microsoft, 
The urlscan.ini file is included as part of URLScan . This sets by default a configuration setting "UseAllowVerbs=1".  In this [AllowVerbs] section of the ini file, only http methods that are allowed are GET, HEAD, and POST so simply by installing URLScan on an IIS server , we can assume that it  protected from TRACE or TRACK.