Populating Listbox using a List which retains its values every time post

[TRINUETEF]

I've got a problem, or well 2 problems which are both related.I have 2 listboxes. In listbox 1 I have Products in and the .SelectedValue is the ItemId from which I can get the Product or the Item. In listbox 2 I want to save the users selected items. My 2 problems : Each time I press the button to add to my other listbox and also display all the content, the List that I have storing the ids is wiped out so it only ever stores 1 value and the 2nd is, nothing is showing up in the listbox. I've been working on this 1 problem for 8 hours and i'm at breaking point. Hopefully somebody can spot my mistake straight away.Here is my aspx page where i'm doing all sorts of stuff to my 2 listboxes and buttons etc.http://pastebin.com/zVqd2G2v^ Lines 12+13 have the 2 lists i'm using^ Lines 63 is my method to get the name of the item by its ItemId (or the value from the 1st listbox)^ at the bottom you can see the button etc.This is my collections class http://pastebin.com/mbmKzUF8There you can see my method that I use on line 113 to get the product from the database which does get the item when I put a break while debugging.If i've been really vague, would like to appologize in advance and I hope someone can spot my silly mistake straight away. Been working on this problem for over 8 hours I think. I'm not sure, maybe more.