My worksheet calculates my timesheet. Each day I enter the time in and the
time out. The difference gets rounded to the nearest quarter of an hour each
day.
(I later add up all the days and do all sorts of other calcs...not important
to this question).

I figure out the rounding by using vlookup with the following formula:
=IF(D9-C90,INT((D9-C9)*24)+VLOOKUP(((D9-C9)*24-INT((D9-C9)*24)),$B$77:$C$81,2),0)

here is the data in b77:c81
0 0
0.13 0.25
0.38 0.5
0.63 0.75
0.88 1

This has been working fine for 2 months now. But, today my time in was
9:00AM and my timeout was 1:00PM and the result was N/A !!!! It works for
9:00 to 1:01 and for 9:00 to 12:00 and for any other combo in the past 2
months.

When I tried stepping throught the formula, it came up to a step doing 4-4
and then came up with the following result to that calc:
-8.88178419700125E-16 !!

I am totally perplexed... Will appreciate help on this one.
I am pretty much a self-taught excel novice...please take that into
consideration when responding. Thanks