function check_popup_form(FormName) {
    var error = 0;
    var errorMessage = "Errors have occured during the submission of this form!\nPlease make the following corrections:\n\n";
    var soldoutMessage = "Sorry, this product size has been temporarily sold out.";

    if (FormName.validityTest.value == "Select Product" || FormName.products_id.value == 0) {
        errorMessage = errorMessage + "* You must select a product from the list.\n";
		error = 1;
    }

    if (isNaN(parseInt(FormName.cart_quantity.value)) || FormName.cart_quantity.value <= 0) {
		errorMessage = errorMessage + "* Your quantity must be greater than 0.";
		error = 1;
	}

    // TODO: error checking on sold out.

    if (error == 1) {
        alert(errorMessage);
        return false;
    }

    if (soldOutProducts[FormName.products_id.value] == true) {
        alert(soldoutMessage);
        return false;
    }

    return true;
}