In previous versions of 4D, when the SET HTTP HEADER(header) syntax was used, the command would accept a literal text type constant as a parameter. For example, you could write:

SET HTTP HEADER("SET-COOKIE: USER="+String(Abs(Random))+"; PATH=/")

This syntax was ambiguous to the point that 4D Compiler could not resolve it. As a result, it is no longer accepted: the header parameter must be a 4D variable or field. If not, a 4D error is displayed in the Web
browser.

Using the previous example, the correct syntax is now:
C_TEXT($vTcookie)
$vTcookie:="SET-COOKIE: USER="+String(Abs(Random))+";
PATH=/"
SET HTTP HEADER($vTcookie)