Excel 2010 – VLOOKUP issue

I have a problem in getting VLOOKUP to evaluate consistently. It is best understood from the screenshot linked (Office 2010), where cells B3 and B4 are not showing the expected values. I wanted to upload the excel file, but cannot see the option to do it.

The screenshot is at http://www.flickr.com/photos/abanerji/8547938172/in/photostream

This is just a small segment of the big excel sheet, and so a global solution is required.

How to get it right please?