Excel 2007 : Baffled by the (lack of) result of a countif

Hi all

I have a baffling problem with a Countif formula on one sheet of a multi-sheet Spread.

Basically, it is sport related, and I have one sheet per year.

The competitors are listed in columns A to C - A is a unique number, B is their name, and C is their team.

In a row at the bottom of this list, I record the fastest - it contains the number of the competitor.

In another row, to the right of the competitors, I count from the 'fastest' row. So for example If competitor 12 was fastest 5 times, it counts and returns 5.
All very straightforward!
Except on one sheet, it is igoring competitors 16 and 17, and returning '0' where there should be 1 in each case.
The formula is:
=COUNTIF($E$30:$W$30,LOOKUP(A17,$A$3:$A$29))
When I step through using the evaluation tool, in all cases (apart from the 2 in question) it evaluates the correct number (1,2,3,4 etc...)
Here is what I get with BOTH of the 2 cells.
COUNTIF($E$30:$W$30,LOOKUP(A17,$A$3:$A$29))
Evaluate
COUNTIF($E$30:$W$30,LOOKUP(16,$A$3:$A$29)) - so far so good it's found '16' !!
Evaluate
COUNTIF($E$30:$W$30,4) - This is the baffling part. Where is it getting '4' from?!

Any thoughts welcomed!

Neil

Solved - there were some erroneous characters used further down the list to try and discriminate other people who stepped in to a team and used the same competitor number!