
Il faut bien sur re-valider le favoris pour relancer la détection automatique du formulaire!
Et utiliser :
http://www.vente-privee.com/vp4/login/portal.ashx comme URL!
Chez moi j'obtiens :
<form method="post" action="http://www.vente-privee.com/vp4/Login/Login.aspx">
<input name="__VIEWSTATE" value="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" type="hidden">
<input value="{nom}" name="ctl00$mainContent$CtlLogin$UserName" type="hidden">
<input value="{mdp}" name="ctl00$mainContent$CtlLogin$Password" type="hidden">
<input name="ctl00$mainContent$CtlLogin$LoginButton.x" value="10" type="hidden">
<input name="ctl00$mainContent$CtlLogin$LoginButton.y" value="10" type="hidden">
<input name="__EVENTVALIDATION" value="/wEWBAKW9oe7CQL2iL3NBwKEsvrWCAKrnaTiCgerv89stEAZ8HLCfKdkaKeXeD4T" type="hidden">
</form>

Et j'viens de re-tester, il me connecte bien sur vente-privee.com !