Multiple Select option in Module pool

Hi,

I wanna add a field for 'Delivery number' in the screen of a mod pool prgm.I created a subscreen area in the main screen and did the coding needed.now the problem i am having is if i giv a single value in the from field or values in the 'From' and 'To' field its not taken to the program,i saw it while debugging. but if i enter the values in the multiple selection option its taken to the program.That means from screen its not going to the program where as from the multiple select option its taken to the program,What may be the propblem.

Regards in Advance,

Nitin