I have a classical report without any module pool. I am validating the fields on the selection screen under the AT SELECTION SCREEN on Field event. On clicking the default execute button on the selection screen for the first time with erroneous values, I am getting the error as expected. But after that, when I press enter with correct values, execution is happening! Which should never be the case. On enter it should stay on the selection screen. Debugging it, I found that first time sy-ucomm value is being set as ONLI on pressing execute button and surprisingly second time on pressing enter also the value of sy-ucomm is ONLI and as a result it is executing the form written for this condition. I have no idea why this is happening. Can someone please throw some light on this and tell me how to solve this?