custom listbox

I have a custom form that has a listbox that is populated from a SQL DB.

No problems there, but when you select an item and hit save the next time you open up the item I would expect to see the item selected; however, this is not the case.

Does anyone know how to do this? If I go to All Fields, the value is actually saved there.

I'm currently just trying to get it to work with a single list, but will eventually need to make it work for a multi select list as well.

Any help appreciated

Thanks.