I've searched all through other posts and have not found anyone with a
similar problem. We have several workbooks that have been set up for at
least 3 years or more. Some of them suddenly, on any given line, will not
return the correct data even though it should be. At first it started with
just a line or two, and then slowly began to increase. At first we thought
the file was corrupt, so we re-created it. That didn't help. Now it has
started doing it in one of our other files--works fine, and then all of a
sudden starts returning zeros.

The formula I happen to be using right now is:
IF(ISERROR(VLOOKUP($A26,BUDGET,5,FALSE)),0,VLOOKUP ($A26,BUDGET,5,FALSE))

Personally, I don't think it's a problem with the formula because the
formulas very from workbook to workbook. It can work fine on line 1 to 25,
quit working for 26 to 30, and then start working again on line 31. It's
bizarre.

Anyone have any ideas?