The data type of true and false result should be the same , try this.
ifthenelse(SQL.Field1 = 0,0.00,Round(SQL.Field2 / SQL.Field1,4))
The data type of true and false result should be the same , try this.
ifthenelse(SQL.Field1 = 0,0.00,Round(SQL.Field2 / SQL.Field1,4))