I have used this and it 'works for me'.
Format([Date], "dddd") & " Week " & DatePart("ww", [Date]) & " of " & DatePart("ww", "12/31/" & [Year])
When I ran with it [Date] and [Year] are fields on a form.
Are you getting an error when you run yours?
I can only think that it doesn't know what...