Using a Credential Provider to log in

Please, somebody explain me how to create a working Credential Provider! I am using the HardwareEventCredentialProvider sample as a base to build my own Provider on top of. I've changed username and password fields, but it seems doesn't work. After submiting credentials to a system I only see a blank screen for a sec. or receive a message "Incorrect password or username" and then authentication starts again... :confused:
What I need to do in GetSerialization() and SetSerialization() methods to log in with existing user? {username=L"virt naXa!", password=L"1234"}

I've read "Credential Provider Technical Reference" and Dan Griffin's article about CPs in Vista and still don't understand how can I log in using credential providers. (May be I've done it not carefully and need to reread them?)

And I'm sorry for my bad English, it's not my native language:)