I tried to add the button in the custom object list view. I've added the button in the search layout too but still the button is not visible in my custom object.can anyone help me how to resolve this issue.... Thanks
Can you please try the following steps again:
Go to the Object>>Look for Search Layouts>>Click on Edit besides the ListView
You will have the buttons listed in the left side box(under Available Buttons) then you will have to move it to the "Selected Buttons" box to see them on the list view which was working fine for mow.