in the eCart object file, find the following:
if (isset($_POST[$this->CartName."_Quantity_".$n])) {
$itemQuantity = floatval($_POST[$this->CartName."_Quantity_".$n]);
}
and change it to:
if (isset($_POST[$this->CartName."_Quantity_".$n]) && is_int($_POST[$this->CartName."_Quantity_".$n)) {
$itemQuantity = floatval($_POST[$this->CartName."_Quantity_".$n]);
}