OK. Let's put the parenthesis back in:
(If {rpt_AddressDetail.Addr1} <> "" then {rpt_AddressDetail.Addr1} + chr(13)) &
(If {rpt_AddressDetail.Addr2} <> "" then {rpt_AddressDetail.Addr2} + chr(13)) &
(If {rpt_AddressDetail.City} <> "" then {rpt_AddressDetail.City} + chr(13)) &
(If {rpt_AddressDetail.State} <> "" then {rpt_AddressDetail.State} + chr(13)) &
(If {rpt_AddressDetail.Zip} <> "" then {rpt_AddressDetail.Zip})
-Abhilash