Excel Lookup Problem.

Lets say I have a spreatsheet like this:

12_11 123
34_15 457
56_18 80
90_21 67

When I am using Vlookup("90_21", range, 2) I get an answer 80.

Ofcourse, my actual spreadhseet is much bigger and different than the above.

Any help why the lookup is looking at one row above the actual row it should
be looking up.

Please let me know if there is a way I can upload the spreadsheet so that I
can let the Gurus troubleshoot more effectively.

Thanks
Mario