I am new to this group, so don't mind if I ask somthing that is too easy for
you. My question is whether
I may use all "standard" Excel 2007 functions. I would like to find interval
in which some function returns
"#NUM!" although it must not, because all parameters are inside "permited
ranges". My idea is to start
with some interval [A, B] for which A is "acceptable" argument and B is
"unacceptable" argument, and,
by halving it (C=A+(B-A)/2.0) and asking : IF C is "unacceptable" argument
THEN B=C ELSE A=C
WHILE (B-A(A+B)/2^32) and my User Defined Function returns A (or B). But
when I use somthing
like (inside my User Defined Function):

Dim X as Double ' and some more variables, not necessary for explanation

and, after that declaration, some assignments ... and :

X=Application.WorksheetFunction.IFERROR(Applicatio n.WorksheetFunction.<_someFunc(<parameters);
-8.0)

(because of my "Local settings" I use semicolumn as arguments' delimiter) in
order to assign to X value of that function
(it is between 0.0 and 1.0 for all values of parameters), or -8.0 if the
function returns "#NUM!", after that I would "ask"
whether X is less than 0.0 (this means that Excel function returns "#NUM!"),
and so on,...

But when I "walk through" my User Defined Function (F8, F8, ... F8) and see
that values of some other variables are
being changed as I expect, when the flow goes to the "sentence" a few rows
above program "crashes" as if the it exited
my UDF.

Please help !!!
Thanks !!!