ASP.NET page postbacks and doesn't get rendered

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ASP.NET

debugging

Hello every1,

I developed and deployed a web application using ASP.NET,C# successfully.
The application was running perfectly until yesterday.
[NOTE: It still works fine on local server (tested using both development server and IIS)]
What happens now is:
The website opens perfectly. After few operations which involves database interactions, in all the pages(except default page), the pages stop responding. I mean, after a few clicks, if I try another operation which involves database interactions, the page starts postback for unlimited time period and never gets rendered. I have validations and exception handling in place.
My default page is a very simple page which accepts user input and saves them into database on submit click.
Having same problem with this page, the only difference being: In this page not even a single database interaction is happening i.e after Submit click the page postbacks for unlimited time period

I would also like to tell that this page checks for page refresh (to avoid duplicate entry) using the code below:

Boolean IsPageRefresh = false;
if (!IsPostBack)
{
    ViewState["postids"] = System.Guid.NewGuid().ToString();
    Session["postid"] = ViewState["postids"].ToString();
}
else
{
    if (ViewState["postids"].ToString() != Session["postid"].ToString())
     {
          IsPageRefresh = true;
     }
     Session["postid"] = System.Guid.NewGuid().ToString();
          ViewState["postids"] = Session["postid"];
}
//in submit click event
if(!IsPageRefresh)
{
    //perform operations
}

I have NO clue why this is happening.
Any help would be greatly appreciated

Thanks
Ankur

(22nd Jan)
UPDATE: I checked event logs on the web server and found an unhandlled exception in the default page (Input Sting not in correct format). I modified a line in the code and its fine now (I don't know why this exception is not caught in my local server).
Now the event log doesn't show any error.
I am still having the same issues described below.
The application doesn't seem to have memory issues. And I haven't reset the IIS.
The website works fine from some of the computers. Now that's ridiculous.
Well I am trying, and if the issue is solved I will post the steps.
Meanwhile Answers from Experts are also welcomed.
(Its an intra-net application newly launched so not much people using it. And the server access is with my boss(the most busiest person in the world) so can't do things fast. :sigh: )
-----------
(27th Jan)UPDATE: I finally got access to web server. Followings points must be noted- 1) There is NO Application Event Log Entry
2) I can browse everything from the web server's browser(ie6), my boss can also browse everything from his system. NO ISSUES.
3) The website CANNOT be browsed from many of the systems in our organisation. The situation is already described below.
4) I checked the memory usage, cpu time - NO ISSUES.
5) The errors that I was talkin about in the 22nd Jan Update below also contains an additional error entry:
<b>aspnet_wp.exe (PID: xxxx) stopped unexpectedly.
Failed to execute the request because the ASP.NET process identity does not have read permissions to the global assembly cache. Error: 0x80131902 </b>(On 22nd Jan).. But as I mentioned no entries after that
--------
Its accessible from machines having Windows Server and not from XP.(My boss n webserver has Win Server loaded)