"OR EAN="
Is missing a space:
" OR EAN="
Use this before the Dlookup
Debug.Print "Article number=" & Article & "OR EAN=" & Standard
Check if you're getting numbers there, if you're getting strings, you need to add apostrophes. I just read those are strings, then try this:
DLookup("Unit", "Article", "Article number='" & Article & "' OR EAN='" & Standard & "'")