in the ps_session.php file located in administrator/components/com_vertuemart/classes i changed the line 503
"$Itemid = "&Itemid=".$this->getShopItemid();"
to
"$Itemid = "&Itemid=1".$this->getShopItemid();"
there is nothing at line 503 but at 548 :
// If we haven't found an Itemid, use the standard VM-Itemid
$Itemid = "&Itemid=" . ($tmp_Itemid ? $tmp_Itemid : $this->getShopItemid());
I have changed for
$Itemid = "&Itemid=1" . ($tmp_Itemid ? $tmp_Itemid : $this->getShopItemid());
but I still have a blank page when products are not found in search box