Asynchronous client script callbacks for iFrames

I'm have an existing ASP.NET application.
In this application i have a web page that contains an iFrame.
This iFrame displays a url link (one of many) that is stored in a text file.  i.e. the text file contains a list of many url's
for example

and on page load using StreamReader class of the .NET framework I loop through each line item of the text file. read the url and store it in a session variable. and pass the first value in the session which in this case is http://screen1.aspx to the iFrame as url to load it for the first time. Next I'm making use of a javascript postback function to reload the page and this time i'm passing the next url to the iFrame so that it now displays this url. i.e http://screen2.aspx

This works fine so far.. however i have some challenges to overcome.. namely..

1. The url to load i.e. for example:- http://screen2.aspx may takes a long time to load..
2. the url mentioned in the text file i.e. for example:- http://screen3.aspx  may not exist.
3. there may be an error in the page while loading the page. i.e. for example:- http://screen4.aspx 

So i have to come up with a different approach to do this.. this is where it gets tricky..

I need to use client callback script (i think) to do a background processing that will asynchronous load the next url i.e. http://screen2.aspx to load in a second iFrame in the background and then display it when the time comes to do so i.e. on javascript postback function without encountering problem 2 and 3 mentioned above. and if it encounters problem 2 and 3 then the background iFrame must asynchronously load the next url in line from the text file. i.e. http://screen3.aspx and so on and so forth.. So that the page displays new screens in the iFrame almost asynchronously without a need of a postback

How can i do this ???

Please help me.. any help in this direction will be greatly appreciated..
Who is Participating?
1. Use AJAX in combination with:
2. You can check if the file exists with File.Exist(Application.PhysicalApplicationPath+"\"+new Control().ResolveClientUrl("screen3.aspx"));
3. Implement an custom errors page in the web.config

I think that covers all the problems you have :)
CollindsouzaAuthor Commented:

Thank you for your quick reply..

But i'm not entirely convinced that the example of codeproject is what i'm lookiing for.. because what is does is.. just disables the screen till it can load the next one.. but i dont want that.. what i want is seemless loading of the next page(url) in the iframe..

Please help!!!
That is impossible to achieve, because you have not enough control of all variables included in websites (loading time, etc..)
Forced accept.

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