Im using the LOOKUP functions a couple of times in a workbook and it works
correctly in all places except one. Here's an example of what is happening:

A B
1 Jane 20
2 Jack 30
3 Stan 40
4 Dave 50

=LOOKUP(Stan, A:A, B:B)

In most places in my spreadsheet the result would be 40. BUT... in one
particular place the result is 30. Can someone help please?