Question: I'm occasionaly getting the following popup from an AJAX.NET application

```
Sys.WebForms.PageRequestManagerServerErrorException: An Unknown error occurred while processing the request on the server. The status code returned from the server was: 12031
```

From the [Microsoft kb](http://support.microsoft.com/kb/193625) that status code indicates a ERROR\_INTERNET\_CONNECTION\_RESET, but it doesn't state what was the underlying issue the triggered the error in the first place.

How can I log/trace/etc the underlying error that generated the popup?

Answer: 
If you're getting that from an updatePanel, set EnablePartialRendering to false in the ScriptManager for the page, and then it should give you the actual error.

Also, if it only happens occasionally, I've found that it could be a viewstate problem, especially when the page goes a long time (20mins or so) between refreshes.

Otherwise, try some try/catch blocks. Those are some easy methods.

Hope that helps!
I had the following error happening on postback:

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

But for me, the issue was that I am converting my project from ASP.NET 2.0 to ASP.NET 4.0 and I had `<asp:UpdatePanel runat="server">` used on the page.

I took off the `<asp:UpdatePanel runat="server">` (for the time being), then ran the page to get the exact error. Which was "A potentially dangerous Request.Form value was detected"

I found that even though I have `ValidateRequest="false"` on the page, ASP.NET 4.0 requires you to add `requestValidationMode="2.0"` in the HttpRuntime tag of web.config.

```
<httpRuntime maxRequestLength="102400" requestValidationMode="2.0"/>

```

[Reference](http://www.codeproject.com/Tips/297679/A-potentially-dangerous-Request-Form-value-was-det)