OK- What I have is an xls file with 2 worksheets (200 and availability) .

The formula I'm using is:

=vlookup($b3:$b202,availability!$A2:$B437,2,False)

'200' B3-B202 a 3 letter code
'Availability' A2-b437 is data(in A) and numeric(in B)

What I want the look up to do is return the numeric value from the
availability sheet to the corrosponding 3 letter code in the 200 worksheet

The data in 200 is static, however the data in availability is copied and
pasted
from another xls file in to the availability worksheet. If the data(ie the 3
letter code) is typed in to availability the formula works, otherwise it
comes up with #N/A.

Is there a formula that needs to be used to format the data?

Thanks in advance for your help!