me21 screen requires editable.

Hi

i maintained User exit mm06E005 for Purchase order creation using ME21. i am facing a problem. i maintained some validations for Po creations. if any wrong data enetered by the user while creation of po using me21. my user exit zxm06u42 will throw an error. in that case my screen will be in display mode. i need screen to be editable to correct wrong entries.

regards

sun