Listbox problems

I am having difficulty trying to work out this problem. After selecting a record in a list box, I have created a command button which opens up a form and allows the user to modify the data. After the user clicks another command button to confirm the update, the user is returned to the orginal form and listbox. However the problem which I am having is that the user cannot then select another record in the list box. The record which is clicked has a frame around it when clicked, but it is not highlighted.

Any help with this matter would be greatly appreciated.
Thanks
James