Password confusion

If I try to install a new printer I need to enter my password but the system reacts as though I'm inputting the wrong password.
I have the same problem if I go to System preferences > Users & groups and try to check / change my password - wrong password message (The shaking box)
In System preferences > Users and groups I see my Apple ID as my family name followed by my christian name (In the box next to where is says 'Full name')
If I access the Apple support site I see my Apple ID as my E mail address and it accepts the password I expect to be able to use.
If I try to overwrite the details showing in Users & groups with my E mail address (Showing as my Apple ID on the help site) I'm unable to do so without entering the password which it doesn't accept.
What am I doing wrong?
It's a Mac OSX Lion 10.7.4

Many thanks

The password you set for your Apple ID has no relation to the password you set for your computer login. The two have absolutely nothing to do with each other. Although it's certainly possible to use the same password if you choose, it's rather obvious you didn't and are using the wrong password to log into your Mac.

You can try the tips in the link below to reset your password:
Forgot Mac Password? How to Reset Your Mac Password (with or without CD)