I noticed that Excel behaves differently when I launch it from access.

I launch access using the following
Set objXLApp = CreateObject("Excel.Application")

I tried to use the yield function (which is an add-in and looking at the
add-ins it is selected), but it returns #name

If I start excel from windows the yield function works fine.  

Is there something special I need to do to activate the add-ins when I
am using excel from Access?

Yes, look at the RegisterXLL method of the Application object in Excel..
Something like:

(xl.RegisterXLL( xl.LibraryPath & "\Analysis\Analys32.xll"))

  -- Dev