(I've commented out the rest of this class and look at
it with application/x-httpd-php3-source .phps)

This parses fine:

if($this->fp = fsockopen($this->SERVER, $this->PORT, &$this->ERRNO, &$this->ERRMSG)):
        fputs($fp, "GET $this->REQUEST $this->PROTO\n\n");
        while(!feof($this->fp)) {
                    $this->result.= fgets($this->fp,128);
            }
         # if($this->DEBUG) { echo $this->result; } 
    else:
        logit( "ERROR: submitting $field[domain] message was: $this->ERRMSG");
endif;

Now uncomment the line with if($this->DEBUG), I get
a parser error. I've noticed this happened to me on
occassion before, but I never got around to paring it
down to a few lines to reproduce it.

Move that exact uncommented line outside of the nesting
if:/endif; block and it also parses fine. In fact, moving
it into the else: block and it also parses fine.