Here are two quotes from Andre Villas-Boas' Wednesday press conference. He said both of these things during the same press conference, less than 10 minutes apart.
When asked whether or not Bale has already been sold to Real Madrid:
"I cannot say anything about that but it is not true."
When asked about the potential Willian transfer:
"I can't really confirm anything regarding Willian. There is interest in the player and there have been conversations."
Generally, when someone says that they can't talk about something, what they mean by that is that they are not going to talk about that thing because they are, for some reason, unable or unwilling to talk about that thing. The word "cannot" or its contraction "can't" implies some degree of seriousness and/or certainty; Andre Villas-Boas didn't say that he 'shouldn't' talk about these things or say that he wished reporters would stop asking these kinds of questions. He said that he is unable to discuss the thing he was asked about, then went on to instantly give out a legitimate answer with real information.
I just found it amusing that AVB has no idea what "cannot" means. Carry on with your day.