Selection screen navigation error in OOPS ALV

Hi ,

In my ALV report I have one selection screen and two normal screen.

                                                                  double click

In this report run like : selection screen---> Screen (1000) ---> screen (2000).

                              screen (1000)again  <,-- Back             <---    Back

From screen 1000 to selection screen it giving dump ( from custome controller object ) if I press Back button.

In debug mode I checked, if I click Back button it again come from PAI(1000) to PBO(1000) again.

In PAI module of 1000 I wrote :

                                            LEAVE TO SCREEN 0.

I also try with : set sclection screen and call transaction ,but giving same dump from selection screen.

Please help.

Thanks,

SK