Password failure after system restore from Time Machine backup

Help! I am locked out of my laptop because the system refuses to recognize my password after a system restore from a Time Machine backup. I have followed onscreen instructions to the letter, tried every combination of solutions and searched the forums in vain.

Sorry for the lengthy explanation that follows, but it was a complicated sequence of events. After trying and failing to eliminate the Spinning Wheel of Death on my 2009 MacBook Pro, I decided to wipe the hard drive and reinstall the OS. First, I backed up all my files (most of them created in Snow Leopard) to my Time Machine.

Next, I did a clean install of the original OS X (Leopard v 10.5) that came with the machine. Then I did a clean install of the Snow Leopard upgrade (v 10.6). Finally, I restored all my files from the Time Machine backup.

After the laptop restarted, everything appeared fixed. The usual login screen appeared with my usual user account name and avatar. I typed in the same password I have used for two years. A progress bar told me it was logging in. Suddenly, up popped a dialog that said: "You are unable to log in to the user account "MyUserAccountName" at this time. Logging in to the account failed because an error occurred."

I did everything I knew to do -- checked caps lock, retyped carefully, went through the "Forgot password" process, etc. Finally, I used the master password to try to reset the user account password and unlock the File Vault. I followed the onscreen instructions: entered a new password, verified the new password, and typed in a password hint. But I got the shaking screen, and the system refused to accept my new password.

So I booted to the install disk and used the Reset Password utility to change the password. The utility told me the new password had been saved. I rebooted to the hard drive, tried to log in with the new password, and once again got the dialog that said: "You are unable to log in to the user account "MyUserAccountName" at this time. Logging in to the account failed because an error occurred."

I just went through the entire OS installation process again, in case I had missed a step. But I've ended up exactly where I started out: with a system that doesn't recognize my password and won't let me create a new password.

Any ideas?

Follow-up to original post-

In case anyone is following this thread, I have contacted Apple phone support. The first guy was unable to help, other than to confirm I had followed all the right steps and that they should have worked. The next guy up suspects that the restoration from the Time Machine backup somehow eliminated my administrator privileges. So I've erased my Mac HD, reinstalled Snow Leopard, created a new user account and am using Migration Assistant to try to migrate my Time Machine backup to the laptop. At this point, however, Migration Assistant is unable to "see" the backup, even though it is now visible in the Finder window. I have a few more options to try and will post a follow-up.

I hope you get this issue resolved. I wonder what is causing it. I wouldn't think Time Machine would reset passwords though. Seems odd. But I don't know much about OS X yet (I've not yet switched from Windows, waiting on money to arrive to buy mu rMBP).

Good luck! Keep us updated.