After finishing the previous Dark Brotherhood quest "Breaching Security", Gabriella tell me to speak to Astrid. However, when I talk to her, the only dialogue I can use is to "ask about her"...

Here are the symptoms I can note (I'm on PC, with latest patch installed) :

• No new quest begins after I talked to Gabriella
  
• all DB NPCs are aroud Veezara, sitting wounded, and talking about Cicero
  
• With the Console, the current stage for the quest (DB07, as found http://www.uesp.net/wiki/Skyrim:The_Cure_for_Madness) is 0
  
• Even when I try to set quest stage or reset quest in the console nothing changes
  
• Loading an older save does not solve the problem.

Does anyone have the same problem?
Can anybody help me?