Informix Error -4420

-4420 The number of lines printed in the IF part of an IF-THEN-ELSE statement

of a header or trailer clause must equal the number of lines printed in the ELSE part.

4GL needs to know how many lines will be filled in header and trailer sections (otherwise it could not know how many detail rows to put on the page). Because it cannot tell which part of an IF statement will be executed, it requires that both produce the same number of lines of output.