HI Nadya,
Thank you for jumping in. Here is the code :

LOCAL nRow
This.Parent.TxtTtlLockerRent.Value = 0
FOR nRow = 1 to This.ListCount
IF This.Selected(nRow) THEN
This.Parent.TxtbaseTtlLockerRent.Value = This.Parent.TxtbaseTtlLockerRent.Value + VAL(This.List(nRow,2))
ENDIF
NEXT nRow

I tried to put it in the When Event with the same results than in the Cklick() event.

Thank you,
Christian Cote