Using XIRR In VBA?

I cannot seem to make my code work. I've used application.worksheetfunction.xirr successfully referring to actual spreadsheet cells, e.g.

VB:
VarIRR = Application.WorksheetFunction.Xirr(Range(Cells(5, 3), Cells(Icount, 3)), Range(Cells(5, 2), Cells(Icount, 2)))

but now, when I'm trying to use arrays instead, it's giving me and error "1004 - Unable to get the XIRR property of the worksheetfunction class."

VB:
tempIRR = Application.WorksheetFunction.Xirr(valueArray, dateArray, 0.01)

I do have the analysis toolpak installed, I've ensured that the date range is seen as date, not text. Number of elements in the value array equals the number of elements in the date array, and I do have negative and positive values..

the full sub of what I'm trying to do:

VB:
Sub CalculateIRR()
Dim i As Integer
Dim j As Integer

[Code]....