I don't know what builds the %form hash and other variables.

Well, that's where you'll have to look, though, because the problem is not in this piece of code.

Update: From your earlier post:

$message .= "<ul><li>Name:$FORM{'name'}<br>\n";

Considering the style of this code, I'd guess that this is some old legacy code. There may be a sub somewhere that sets up the %FORM hash.

Please edit your nodes to add <code> tags around each piece of code and input/output.