So your problem is using a non-unique value for your search. I made a few changes. Your listbox did not specify the width for the last column, so I set it to 80, and added another 0 width column.
ColumnWidth property for lstLookup now reads: 100 pt;60 pt;40 pt;80 pt;70 pt;80 pt;0 pt
Then I added one line to your search button code:
This means that now you have the row number of the search results available to do your textbox updating. Which requires a change to the double-click event for your listbox (changed it as little as possible):
Bookmarks