I have doubt in multiselection..Its urgent

Hi All,

I have a table having four fields...They are

1> DocumentNo.

2> Amount

3> Description

4> Date

I have to implement multiple selection.

And if the amount is negative then I have to display a message"Installment Plan cant b created"

And on multiselection or on single selection I will be passing the documentno to the BAPI.

I have implemented the logic..But its not working.

So as per the requirement,I need it urgently..Kindly help me with the logic and the code snippet

Regards

DK