how do I disable Button asp.net

You can use the client-side onclick event to do that:

yourButton.Attributes.Add("onclick", "this.disabled=true;");

or

You can do this with javascript. in your form tag,

onsubmit="javascript:this.getElementById("submitButton").disabled='true';"

or

In code behind file you can do like this

button1.enabled = false 

You have to disable it on client so that user could not click it again.

<asp:button id="btn" runat="server" OnClientClick="this.disabled=true;"......

To disable on server side asp.net code.

btn.Enabled = false;