lost password, can't authenticate

not a bug, converting to question

Are you two sharing one user account, or do you each have your own?

I don't remember user and password what i can do

You can do this: http://www.psychocats.net/ubuntu/resetpassword

or

To discover your user and restore (change) the password you can:

Start the pc the when you see the GRUB row...

Press ESC.

Press "e" for edit.

Highlight the line that begins kernel ………, and press "e"

Go to the very end of the line, add rw init=/bin/bash

press enter, then press "b" to boot your system.

Your system will boot up to a passwordless root shell.

Type in grep -i 1000 /etc/passwd

The system must show a row with your user name at the start of the row
for example:
danilo:x:1000:1000:ubuntu,,,:/home/danilo:/bin/bash

Here my user is danilo

Then to change your user password type in:

passwd username

or

passwd -d username

change username with your real user

Set your password.

Type in:

reboot

or

reboot -f

Hope this helps

Annette suggests this article as an answer to your question:
FAQ #356: “How do I reset my password in Ubuntu ?”.

i have a user name and password and can get into the system no problem but when i want to change my wireless conections its asking me to authentication password and i change this to a different password and i cant remember it.How do i reset this