Hi Rohit,
From the first screen when you click on execute you are directed to the second screen, but you are not clearing the sy-ucomm. The best option is to use an ok_code and clear the ok_code after the PAI of first screen. Inn the second screen use the ok_code of the second screen for checking the enter event. You may also clear the sy-ucomm valu in the last of PAI of your first screen. But it is not recommended to clear a system field.