JavaScript Object Expected Error In _doPostBack('','')

I keep getting the 'Object Expected' error within my page script when I click the button. I've debugged using fire-bug and the id passed to the JavaScript method is the correct id

Solution 1:

the dopostback method is with two underscores not one, like

__doPostBack

so your call is like:

__doPostBack(btn.id, '');

instead of

_doPostBack(btn.id, '');