Disabled = true does not work in code behind

There's a weird character in the markup:

önserverclick

Please try it this way:

protected void btnSend_Click(object sender, EventArgs e)
{
    if (Page.IsValid)
    {
        btnSend.Attributes["disabled"] = "disabled";
        System.Threading.Thread.Sleep(2000);
    }
}

And as already observed the ö should be an o.

Cheers!

I don't know what you want to do by putting the thread to sleep.
If you wanted to disable the button for 2000 millisecond, it is an incorrect approach.
If you want just wait 2000 millisecond and then disable the button, it works.
Here is the code:

<button id="btnSend" runat="server" alt="" causesvalidation="false">
            <span><b class="va">Send Message</b></span>
        </button>

protected void Page_Load(object sender, EventArgs e)
       {
           this.btnSend.ServerClick += new EventHandler(btnSend_ServerClick);
       }
       void btnSend_ServerClick(object sender, EventArgs e)
       {
           btnSend.Disabled = true;
           System.Threading.Thread.Sleep(2000);
         
       }

If you want to make sure the user doesn't click twice in rapid succession you would have to handle this on the client side in javascript. Sleeping on the server side is not going to help you here. Try it along the lines of this here sample:

<button id="btnSend"  runat="server" alt="" CausesValidation="false"  onserverclick="btnSend_Click" onclick="lockButton(this)">

<img id="imgSend" alt=""  runat="server" src="~/Images/Buttons/send_ico.gif"
align="top" />
<span><b class="va">Send Message</b></span>

</button>

and on your page you need some javascript:

function lockButton(button)
{
    button.disabled = true;
}

Since you also have a server side function that will be executed you'll not even have to worry about resetting the value to false. When the page has made the roundtrip back from the server the button will be enabled again unless you chose to do other wise.

Cheers!

<pre lang="cs">protected void btnSend_Click(object sender, EventArgs e)
{
    if (Page.IsValid)
    {
        btnSend.Disabled = true;
        System.Threading.Thread.Sleep(2000);
    }
}

this code can not working in code behind(ASP.NET). because ASP.NET have not properties Disabled.
that It use visible and enabled.
You can use code below

protected void btnSend_Click(object sender, EventArgs e)
{
    if (Page.IsValid)
    {
        btnSend.Visible = False; //button is hidded
        System.Threading.Thread.Sleep(2000);
    }
}

or

protected void btnSend_Click(object sender, EventArgs e)
{
    if (Page.IsValid)
    {
        btnSend.Enabled = False; //button is hidded
        System.Threading.Thread.Sleep(2000);
    }
}

good lucky!

Try removing CausesValidation="false" or Set the CausesValidation="true"