Post your formula... there is no constraint on index match. That being said
index match is about 5% slower than VLookup...

http://www.decisionmodels.com/optspeede.htm

That being said index match is IMO the way to go for many reasons most
noteably it is far less prone to error than VLookup.

My best guess at your problem would have to with absolute vs relative
references.
--
HTH...

Jim Thomlinson


"Ken" wrote:

Excel2003 ...

My understanding is ... an array "Index/Match" Formula calculates faster
than a "VLookup" Formula ... If so, then I would like to use "Index/Match".
Also, I often do use "Index/Match" as the Index can be either R or L of
target cell.

Issue ... with 2 Cols of 40,000 records ... Index/Match Formula fails to
copy all the way down the 2nd Col ... It seems to fail @ about 20,000 records
down the 2nd Col (one clarifier ... I am on the same WorkSheet ... adjacent
Cols)

Above said ... Am I up against an "Index/Match" constraint here ... or ...
as is generally the case ... Is this an oversight on my part?

Please enlighten me ... Thanks for the guidance ... Kha