I faced this problem while upgrading .net 2.0 website application so that it may be used in VS 2008 but target framework as .net 2.0 and not 3.5. When I tried to compile the application I got following error.

'Could not load assembly or type System.Web.Extension....". I figured out that I don't have Asp.Net ajax extension installed. When I tried installing ajax extensions I got the title error again and again. After some googling I applied various suggestions like run the msi as administrator (FYI I was using VS 2008 in Windows Vista). Finally one solution worked i.e. the service Ngen was not running in my machine due to which installation action was being rolled back. So make sure you have this service running before you install Asp.net AJAX 1.0. See this forum for more info...

http://forums.asp.net/t/1069586.aspx?PageIndex=2

As suggested by Louis.Lu there is another work around if above method doesn't work

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hello, i'm from china, my english is nood good,

i think i could help you.

first, you double click "ASPAJAXExtSetup.msi", copy the following files to other places before the installation has errors.
  C:\Program Files\Microsoft ASP.NET\ASP.NET 2.0 AJAX Extensions\v1.0.61025
      AJAXExtensionsToolbox.dll
      System.Web.Extensions.Design.dll
      System.Web.Extensions.dll

second, copy the above files to "C:\WINDOWS\assembly"

finally, you go installation "ASPAJAXExtSetup.msi" again.

I succeeded like this.

 ----------------

Why Do That:

----------------

Because natural language processing without understanding the underlying emotions is impossible. 

What:

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Okay, so lets start understanding this by trying to find an answer to this question:

I guess, still no web search(??) takes as an input a question and understands the question and does a search for answers to that.
How to do that ?

The application to such is manifold. For example, some govt. agencies might be interested in finding "How many red cars exist in Bangalore?"

Or, some legal intercept developer wants to intercept all the communication by just typing in "What people are talking about New Delhi and violence?"

Etc. Etc.

Remember, after some incidents, police asks for help in investigation. Some people approach the police after that, saying they saw some people acting  "suspiciously". How are we able to process these things ? Can we make a "machine" capable of doing that ?

Reference:

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Computer_method_and_apparatus_for_extrac.pdf
Monte_Carlo_method_for_natural_language_.pdf
Probabilistic_system_for_natural_languag.pdf
Search_engine_with_natural_language_base.pdf
Systems_and_methods_for_word_recognition.pdf

I face this requirement few days before so first of all I will discuss some of the scenarios where we need to use table name as a variable.....

Why We Need Table Name As Variable: While developing an database application incrementally, at the last, mostly we have a bad designed database and mostly we have a repetitive scripts for the same task, these things happen due to lack of the foresight and lack of the big picture of the application, any way to avoid the same scripts for the same task that include the different tables we should have to use this concept. The things will be clearer with the example given below.

How Table Name Can Be Used As Parameter: Let’s take an example to make things more understandable, suppose we are getting the information of the hotels from different hotels groups, and due to the difference in the feed formats we are storing the information in the tables with respect to each group, now our requirement is to get all the hotels irrespective of the hotel groups for a particular pin codes. For this we need to check all the tables with respect to hotel groups so here is the store procedure that simply took the table name and pin code as a parameters and provide the desired result set, the way to do it is to create a string of the script and execute it.

   1:   

   2:  CREATE PROCEDURE sproc_GetHotesForPinCode

   3:  @tableName varchar(100) , 

   4:  @pinCode varchar(10) 

   5:  AS 

   6:  BEGIN 

   7:  DECLARE @sqlScript varchar(2000);

   8:  --Building up the sql script ;

   9:  SET @sqlScript = 'SELECT * FROM ' + @tableName + ' 

  10:  WHERE Pincode = ' + @pinCode ;

  11:  --Exec the sql script ;

  12:  EXEC(@sqlScript);

  13:  END

  14:  ;

I converted one ASP application to VB.Net using Microsoft ASP migration assistant utility. It was interesting
to see that the utility created all the required interop dlls for my unmanaged COM components. so I saved my time in
running tlbimp on each COM/EXE/DLL(unmanaged) or by using Visual studio. Cool Eh!!
I found one very interesting and quite unexplored issue (atleast i didnot get much on googling  ) that was                                                                                           my call from managed environment to unmanaged got failed for no obvious reason. Prima facie, I got feeling
that it happened due to some wrong marshalling of data which eventually proved true.

Let me staright jump into the issue by one example and explain its fix.

my backend (C++) has one API implementation something like this

CFoo::CreateMyList(

                        /*[in]*/   VARIANT*                     vSomeInVaiant,

                        /* [out] */ VARIANT*             pvSomeOutVariant,

                        /* [in] */ BOOL bSomeBoolean,

                         BOOL*                         bRetVal )

my default VB.Net code (after conversion) was something like this,

blnRetVal = CFoo.CreateMyList(vSomeInVaiant, vSomeOutVariant, bSomeBoolean)

this call was ending up in some unhandled exception resulting a crash in application. To dig more I disassembled
my interop. I found the intermediate signature in my interop dll something like this

.method public hidebysig newslot abstract virtual

        instance int32  CreateMyList([in] object  marshal( struct) vSomeInVaiant,

                                            [out] object&  marshal( struct) pvSomeOutVariant,

                                             [in] int32 bSomeBoolean,

                                             ) runtime managed internalcall

{

  .custom instance void [mscorlib]System.Runtime.InteropServices.DispIdAttribute::.ctor(int32) = ( 01 00 03 00 00 00 00 00 )

} // end of method IFoo:::CreateMyList

 when I hardcoded vSomeInVaiant in backend, everything worked fine. that meant the runtime marshaller is not able to do
 his job properly for in variant. I donot owe to whatever fix I am going to tell you now.

 I read it somewhere that by default VB.Net passes everything byref so I needed a way to pass it byVal. I found a workaround.
 you enclose your variant (I'm sorry Object in managed env.) inside parantheses. that will make your runtime to evaluate it
 as an expression first and then it will be forced to pass byVal.
 
 the next thing i did was
 
 blnRetVal = CFoo.CreateMyList((vSomeInVaiant), vSomeOutVariant, bSomeBoolean)
 
 believe me the trick worked seamlessly. I applied this trick everywhere in my project and it worked.
 
 To summarize it,
 
 pass in variant enclosed in parantheses
 pass out variant as it is
 pass in/out variant ( never tried so far  ), you need to let me know.
 
 I am open to more discussion on this. I will be obliged for any comment.

Reference: http://aspnettechstuffs.blogspot.com/
    

Problem: Try creating one form inside an update panel. Put some validators like RequiredFieldValidator etc. Also put in LinkButton insite the update panel. You will notice when you click on the linkbutton nothing happens.

Reason: When you try to submit the form or doing postback, a few javascript client side functions are raised due to validators and due to some error validation fails and postback event is not raised. 

Solution: There is some problem with the code validators have been written. Check the following post http://blogs.msdn.com/mattgi/archive/2007/01/23/asp-net-ajax-validators.aspx

So untill some windows update is not release you're stuck with it. However there is a work around with some limitations. Set the enableClientScript = "false" for all validators. This will disable the client validation and post back event is raised. Since any way you are using update panel, the validation will occur on server side and you will get the same result and without noticeable delay. With this work arround you are losing the client validation but I think still it's okay because you will still be able to use the validators inside update panel. 

Hope this helps!