Deauthorize Audible Account

I've already looked at some posts about this issue, but it still doesn't solve my problem.
I have 2 MacbookPros in my household. For some reason I choose to install my Iphone 3G to computer B instead of A (primary computer). I used iTunes 7.7

*Computer A (primary)*
Now i'm having problem to get the authority on my main computer, it says:
iTunes Store/ Account.
+Computer Authorizations: One machine is authorized to play music purchased with this account.+

*Computer B (secondary)*
Now I choose to "Deauthorize Audible Account" (in the advanced menu). Which I think it means the same Apple ID-account I use to login to iTunes, right? Pop-up window comes up, I have to enter +"Audible user name" & "Password"+.

Still doesn't work. It claims it's wrong user name or password. Which is not.

Any ideas?
Thanks for your help.