Anyways this answer is too late, but still I'm posting may be it be helpful for others. The search query should be written in specific pairs as mentioned in the above PDF file like
$search = $rets->Search("Property","RESI","(MLNumber=0+),(StatusDate=2013-06-01-2013-09-01)");
IMPORTANT: This is for rapattoni mls, this may differ from MLS to MLS.
I hope this would be helpful to someone.