How come this doesn't work?

=IIf(IsNull([txt_cumulamt7]),"",IIf([txt_cumulamt7]050,"","Benefit
Recognized"),IIf([txt_cumulamt7]1,"",""))

If the field is Null, then nothing appears
If the field is less than 50, but more than 0 then Benefit Recognized
If the field is 0, then nothing goes in the box
Thanks in advance!