Question Using Date Difference Function for MSProject Addin

[jaksel]

I am creating a Microsoft Project 2007 Add-In using VS2008 and VB.NET. So far, so good.
I am trying to access the Member Function DateDifference

The function returns the number of Business Days within the specific MS Project file between two given days. It respects the calendar assigned to the project including holidays, etc.

I can find the function in the object browser here:

Microsoft.Office.Interop.MSProject._MSProject
It returns a value of Long

And the intellisense lets me get that far. However, I am trying to do this:

mProj As Microsoft.Office.Interop.MSProject._MSProject.DateDifference( Date1, Date2, CalendarName)

But that appears to be not allowed.

Any ideas on how I can correct this?

Thanks