Catching "Maximum request length exceeded"

As GateKiller said you need to change the maxRequestLength. You may also need to change the executionTimeout in case the upload speed is too slow. Note that you don't want either of these settings to be too big otherwise you'll be open to DOS attacks.

The default for the executionTimeout is 360 seconds or 6 minutes.

You can change the maxRequestLength and executionTimeout with the httpRuntime Element.

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <system.web>
        <httpRuntime maxRequestLength="102400" executionTimeout="1200" />
    </system.web>
</configuration>

EDIT:

If you want to handle the exception regardless then as has been stated already you'll need to handle it in Global.asax. Here's a link to a code example.

There is no easy way to catch such exception unfortunately. What I do is either override the OnError method at the page level or the Application_Error in global.asax, then check if it was a Max Request failure and, if so, transfer to an error page.

protected override void OnError(EventArgs e) .....


private void Application_Error(object sender, EventArgs e)
{
    if (GlobalHelper.IsMaxRequestExceededException(this.Server.GetLastError()))
    {
        this.Server.ClearError();
        this.Server.Transfer("~/error/UploadTooLarge.aspx");
    }
}

It's a hack but the code below works for me

const int TimedOutExceptionCode = -2147467259;
public static bool IsMaxRequestExceededException(Exception e)
{
    // unhandled errors = caught at global.ascx level
    // http exception = caught at page level

    Exception main;
    var unhandled = e as HttpUnhandledException;

    if (unhandled != null && unhandled.ErrorCode == TimedOutExceptionCode)
    {
        main = unhandled.InnerException;
    }
    else
    {
        main = e;
    }


    var http = main as HttpException;

    if (http != null && http.ErrorCode == TimedOutExceptionCode)
    {
        // hack: no real method of identifying if the error is max request exceeded as 
        // it is treated as a timeout exception
        if (http.StackTrace.Contains("GetEntireRawContent"))
        {
            // MAX REQUEST HAS BEEN EXCEEDED
            return true;
        }
    }

    return false;
}