My situation is this:

Row 6, from column D to column DT, is a set of dates in ascending order.
Columns D through AY are dates in 2006. Columns AZ through DT are dates in
2007. Cash flows are in rows 9 through 100 (one row for each investment).
EA9:EA100 has the December 31, 2006, values; EB9:EB100 has the December 31,
2007 values. EA6 is equal to the date December 31, 2006; EB6 is equal to the
date December 31, 2007.I would like to calculate the XIRR for 2007 by using
the inverse of the December 31, 2006 value as the first cash flow. I'm
trying to do it as, e.g.,

XIRR((-EA9,AZ9:DT9,EB9),(EA6,AZ6:DT6,EB6))

I'm getting a #VALUE error. Is there some means other than an extra set of
parentheses to specify that the set of references is to be treated as a
single argument?