implementing user exit

Hi Abappers,

I am trying to implement a customer defined validation in the user exit EXIT_SAPFP50M_002 in PA30 transaction. I want to display a particular error message, if the particular wage type is entered in the second screen(2010), but after displaying the error, the screen fields get greyed out. i want to enable the user to edit the fields after the error message has appeared. How should i do this? please suggest me a solution.

Regards

Naren.