Try this:
[font="Courier New"]if not exists (select name from sys.objects where type_desc = 'DEFAULT_CONSTRAINT' and name = 'DF_AID_AGENCY_STAFF_CSR')
ALTER TABLE dbo.AID_AGENCY_STAFF ADD CONSTRAINT DF_AID_AGENCY_STAFF_CSR DEFAULT 0 FOR CSR
[/font]
MARCUS. Why dost thou laugh? It fits not with this hour.
TITUS. Why, I have not another tear to shed;
--Titus Andronicus, William Shakespeare