On Sun, 24 May 2009 00:20:00 -0700, Jerry Mitchell <Jerry
wrote:

The subject pretty much says it all, this is happening, and there's a valid,
plain integer value in I4, and manually entering said value does the same
thing... I don't get it.

If I2:I11 is not sorted in ascending order, you can certainly get #N/A values.
In some quick testing with Excel 2007, it seems to be the case that if I4
contains a lower value than I2 and I3, LOOKUP will return #N/A.

If your values are not sorted, and you are looking for an exact match, try
VLOOKUP instead:

=VLOOKUP(I4,I2:I11,1,TRUE)

--ron