full post back occurs

Well you will need to remove unnecessary stuff and recheck code since everything is fine then problem is in your code. So try creating a new page and one by one put all things there

there i one more issue regthe scrippt & post back issue on button click

as i said grid header when clicked fires a javascript which has button click event

the button click event has code for making few other controls visible true / false depending on the values

so suppose i click the header & a dropdown is visible = true

without clicking on any other control , i click another column header the script doesnot fire

i hope i am clear

Why don't you hide and show controls using javascript rather than doing it from updatepanel

 mean on client side  using script

i cant as i have to do some data checking frm database before displaying

but why this behaviour of the control in update panel??

So this is what you can do

1. Create a hidden field

2. Based on your checking store value true or false in the hidden field

3. Using javascript read the value of hidden field. If true show controls if false hide controls