The fix can be corrected by: Changing line 437 in /js/varien/js.js

 

var error = false, day = parseInt(this.day.value) || 0, month = parseInt(this.month.value) || 0, year = parseInt(this.year.value) || 0;

to

var error = false, day = parseInt(this.day.value, 10) || 0, month = parseInt(this.month.value, 10) || 0, year = parseInt(this.year.value, 10) || 0;

Big thanks use IgorKaiders from the Magento Forums in this post for the fix.