Just to follow up the search was still not working until I changed the "s" to "t" like so:
$search_rsDataSet->setSearch(array("type"=>"Value", "comparison"=>"<=", "join"=>"AND"), array("pbm.EffectiveDate"), "t", isset($_POST["effectivedate"])?$_POST["effectivedate"]:'');
$search_rsDataSet->setSearch(array("type"=>"Value", "comparison"=>">=", "join"=>"AND"), array("pbm.ExpirationDate"), "t", isset($_POST["effectivedate"])?$_POST["effectivedate"]:'');