Custom screen field not displayed in the Screen ME21n

Hi,

I created a custom screen field in ME21n and tried creating purchase order with data in the custom screen field, I was succesfull in updating the table with the custome field data in the table but when i tried creating a purchase order by giving the reference document number (Existing Purchase order) which has the custom field data I am not able to see the custom data in the screen but i could find rest of the data in the screen. Can any one help me on this? what could be the reason?

BR,

Sudheer