error when checkout cart

[stephen0830]

there error when checkout cart as below:
A Database Error Occurred
Error Number: 1366

Incorrect Decimal Value: '' For Column 'Tax_amount' At Row 1

INSERT INTO `Jem_invoices` (`Product_type`, `Payment_status`, `Order_status`, `Member_id`, `Customers_name`, `Customers_company`, `Customers_address_1`, `Customers_address_2`, `Customers_city`, `Customers_postal_code`, `Customers_state`, `Customers_country`, `Customers_telephone`, `Customers_primary_email`, `Coupon_code`, `Date_purchased`, `Due_date`, `Sub_total`, `Ip_address`, `Referrer_id`, `Tool_type`, `Tool_id`, `Invoice_notes`, `Discount_amount`, `Shipping_name`, `Shipping_company`, `Shipping_address_1`, `Shipping_address_2`, `Shipping_city`, `Shipping_postal_code`, `Shipping_state`, `Shipping_country`, `Shipping_method`, `Tax_amount`, `Shipping_amount`, `Tracking_id`, `Cc_four`, `Cc_month`, `Cc_year`) VALUES ('Physical', '0', 'Order_pending', '2', 'Stephen Sit', '', 'B-15-7, Aman Heights Resort Condominium', '', 'Seri Kembangan', '43300', 'Alabama', '129', '+60165997954', 'Stephen@Sncetech.Com', 0, 1433892714, 1433921514, 499.95, '219.92.7.113', '0', '0', '0', '', 0, 'Stephen Sit', '', 'B-15-7, Aman Heights Resort Condominium', '', 'Seri Kembangan', '43300', 'Alabama', '129', 'Flat Rate', '', 7.5, 0, '', '', '')

Filename: W:\Xampp\Htdocs\Glispa\System\Database\DB_driver.Php

Line Number: 330

[forumadmin]

please install JEM on a linux / unix based host