In the language used to create Load scripts, there are actually two constructs to conditionally execute code or evaluate expressions.
There is the IF THEN ELSEIF ELSE END IF control statement which can only be used amongst other statements and follows typical statement formatting logic. You can omit the ELSE and ELSEIF parts but not the others. See: If..then..elseif..else..end if - QlikView
And then there is the IF() function. That one - like any well-behaving function - takes parameters. You separate the parameters with commas, and the function returns a value. Since IF() takes a variable number of parameters, you either specify two or three parameters, not more, not less. See: if - script and chart function - QlikView
What is it you want to do exactly?
PS Apparently Qlik is further cleaning up its act, because the help doesn't talk about the two-parameter IF() version anymore. But it should still work...