Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server."

This issue for me was caused by a database mapping error.

I attempted to use a select() call on a datasource with errors in the code behind. My controls were within an update panel and the actual cause was hidden.

Usually, if you can temporarily remove the update panel, asp.net will return a more useful error message.

" 1- Go to the web.config of your application "

" 2- Add a new entry under < system.web > "

<httpRuntime requestValidationMode="2.0"/>

3- Also Find the pages tag and set validateRequest=False

Only this works for me. !!

Check your `Application` `Event Log` - my issue was `Telerik RadCompression` HTTP Module which I disabled in the Web.config.

Be sure to put tilde and forward slash(~/) when CDN is the root directory. I think it's an issue in IIS

I also faced the same issue , and none of these worked. In my case this was fixed by adding these lines in config file.

<appSettings>
<add key="aspnet:MaxHttpCollectionKeys" value="100000" />
</appSettings>

<system.web.extensions>
<scripting>
<scriptResourceHandler enableCompression="false" enableCaching="true"/>
</scripting>
</system.web.extensions>

I had this issue and I spent hours trying to fix it.

The solution ticked as answered will not fix the error only handle it.

The best approach is to check the IIS log files and the error should be there. It appears that the update panel encapsulates the real error and outputs it as a 'javascript error'.

For instance my error was that I forgot to make a class [Serializable]. Although this worked fine locally it did not work when deployed on the server.

We also faced the same issue, and the problem could only be reproduced in the server (i.e., not locally, which made it even harder to fix, because we could not debug the application), and when using IE. We had a page with an update panel, and within this update panel a modalpopupextender, which also contained an update panel. After trying several solutions that did not work, we fix it by replacing every imagebutton within the modalpopupextender with a linkbutton, and within it the image needed.

@JS5 , I also faced the same issue as you: ImageButton causing exceptions inside UpdatePanel only on production server and IE. After some research I found this:

> There is an issue with ImageButtons and UpdatePanels. The update to
> .NET 4.5 is fixed there. It has something to do with Microsoft
> changed the x,y axis of a button click from Int to Double so you can
> tell where on the button you clicked and it's throwing a conversion
> error.

[Source][1]

I'm using NetFramework 2.0 and IIS 6, so, the suggested solution was to downgrade IE compatibility adding a meta tag:

<meta http-equiv="X-UA-Compatible" content="IE=9" />

I've done this via Page_Load method only on the page I needed to:

Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
Dim tag As HtmlMeta = New HtmlMeta()

tag.HttpEquiv = "X-UA-Compatible"
tag.Content = "IE=9"

Header.Controls.Add(tag)
End Sub

Hope this helps someone.

[1]:

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as my friend @RaviKumar mentioned above one reason of following problem is that some piece of data transferred from code to UI contain raw html tags which make request invalid for example I had a **textarea** and in my code I had set its value by code below

`txtAgreement.Text = Data.Agreement`

And when I compiled the page I could see raw html tag inside textarea so I changed textarea to **div** on which **innerhtml** works and render html (instead of injecting raw html tags into element) and it worked for me

happy coding

<add key="aspnet:MaxHttpCollectionKeys" value="100000"/ >

Add above key to Web.config or App.config to remove this error.