Date Available: when entered does not save

What version of Zen Cart are you using? 1.5.1
Has your site been upgraded? When? From what version(s)? 1.3.8
If you've upgraded, HOW did you upgrade? (official upgrade procedure or an automated script from your hosting company?) Yes all fine and working ..except
What plugins/addons have you installed? See list below.
tzf_v1.00
mailchimp_3.0
Keepalive Timer
Image_Handler4_v4_1
easyslider1.7
Add_Phone_Number_on_Contact_Us.6

What version of PHP and MySQL is your server using? (See Admin->Tools->Server Info) PHP Version: 5.3.20 (Zend: 2.3.0) PHP Memory Limit: 128M
WHEN did the problem "start"? Just noticed as I have never used it before,

Now my problem. During adding or editing a product, Date Available: when entered does not save. I can select the date but it is not saving it.

Can you please point me to the right direction to fix this problem.

Thank you.

OK I made a minor (date('Y-m-d') change and it fixed the problem in case someone else has the similar problem.

admin > includes> modules >update_product.php

Changed >> $products_date_available = (date('Y-m-d') < $products_date_available) ? $products_date_available : 'null';

To >> $products_date_available = (date('d-m-Y') < $products_date_available) ? $products_date_available : 'null';