I'm experiencing the nuisance that is the "arithmetic overflow converting
expression to int" error, but I'm not seeing this error consistently enough
to think there's something wrong with my code.

Here's the snippet:
select round((sum(gu)/50000),2) as gu_aal,
round((sqrt(((50000*sum(gu_square))-square(sum(gu)))/(50000*49999))),2) as
gu_stdev

The first field is basically an average, while the second is a specialized
standard deviation.

I use a bit of VBA to extract the result of this query. So, when I hit the
play button to let the function run, the error pops up and stops my function
dead. But, when I hit F8 and step through the function, it works perfectly.
To me, that makes no sense. The code never changes, so why would it run using
one method but not the other?

Can anyone shed some light on this problem?