I have been repeatedly asked about how to prevent users from clicking submit button more than once. If you have ever faced such a problem, you would probably know that there are many ways suggested by folks to handle this, things like using two buttons, disabling submit button using JavaScript and so on. Regrettably I never did find anything that worked like they said it would and more importantly some of those methods causes your server side events not to fire. The way I deal with this issue is not just disabling the button by greying it out, but not letting the form to be posted back using the code below:
1) Put this in between the HEAD tags of your page:
<HEAD>
...
<SCRIPT language=javascript>
var isSubmittedFlag= false;
</SCRIPT>
...
</HEAD>
2) Add the following java script code to the button attributes collection in Page_Load() event of your page
btnSubmit.Attributes.Add("onclick", "BLOCKED SCRIPTif(isSubmittedFlag){alert('Your first request is still being processed');return false;}else{isSubmittedFlag=true;return true;}")