From http://www.spip.net/en_article3980.html:
"When SPIP sees the tag #FORMULAIRE_CONTACT, it recognises it as a tag of the type #FORMULAIRE_xxx. So it looks for the template formulaires/contact.html in order to display the form."
Well, SPIP may look for the template contact.html but it won't find it because it doesn't exist, at least not in SPIP 2.0.9 [13982].
What can I say when SPIP asks me where it is?