>>How can I do it?
>
>The events are all listed in the Properties window (click the button with the lightning icon)

Finally was able to test - the Remove button seems to work.

The Cancel button with my js HideElement code doesn't work, though :(

It has OnClientClick

HideElement('<%=tblProInfo.ClientID %>');

But it shows null for me

function HideElement(what)
{
var x = document.getElementById(what);
alert(x);
if (x) {
  x.style.display = 'none' ;
  }
  return true ;
 }