AsyncPostBackSourceElementID not working with HTML Button?

Hi

I am not able to find the ID of HTML Button using code below.

If I click button  it won't  work. [obj.AsyncPostBackSourceElementID --> should have ID of HTML Button]

If I click button simantaneously10 times I get the data to be displayed.

Thank You

ScriptManager obj = (ScriptManager)Master.FindControl("ScriptManager1");                              

if (obj.IsInAsyncPostBack)

{                                  

switch (obj.AsyncPostBackSourceElementID)

.........

}