Europe SUMPRODUCT Function

[braydon16]

I have a workbook that I've developed here in the US for use in Europe. I'm having issues with one particular SUMPRODUCT function. In a sense, the file is a tracking log. The user can input dates in column B and select a persons name from a validation list in column D. For some reason the following function works fine in the US, but not for some users in Europe.

=SUMPRODUCT(--('Tracking Log'!$D$6:$D$5000=$C13),--(TEXT('Tracking Log'!$B$6:$B$5000,"yyyym")=Data!$A$17&MONTH($E$11)))

Data!$A$17 is the current year and $E$11 is the month.
I assume that it could be due to the date format, but am not positive. The dates in column B are all formatted for Europe ("dd/mm/yyyy").

Any ideas?