(SOLVED!) Here's how to solve Taobao system's busy error 淘宝问题；系统太忙了，的解决方法

Facing the above? Do the following:
- reduce the number of items in your cart (i.e. cart out less items).

If the above (which work most of the time) did not work for you, then,
- one of the items in your cart is the problem, find it and remove it/replace with another seller - more hassle but it works :)