A backup archive was created on an external hard drive in Ubuntu. Debian 6.0 was installed on the machine. After configurayion, an attempt was made to access the backup archive. None of the passwords worked. The caps lock and numlock were checked. How can I get past this?

What did you use to encrypt the backup and make the backup in the first place?

It's a good thing you tested your backup/encryption strategy after creating the backup. Unfortunately, many people don't. Just create another backup from the original source. Being very attentive to detail in your second attempt. If this second attempt fails, I'd look at different backup and different encryption software. But most likely, it was user error somewhere in the mix of your first attempt. Typically, the password you think you used is not the password you actually used. Some typo occurred. I've had a coule of incidents over the years where I'd swear up and down that I knew the password exactly, yet I couldn't make it work.

Oh wait, I think I might have misread your initial post. When you said you installed Debian, was that AFTER you had done the backup, so the original data used to make the backup was overwritten? If that's the case, the problem is much more severe. Trying to unencrypt a backup without the key will most likely be impossible.

I think I would try doing some guessing at the password. Try to figure out what a likely typo might have been that you could have made in entering the password initially. Hopefully with enough brute force guessing at slight variations of the password you thought you entered, you might be able to stumble upon the one that actually got used. A common mistake is to swap the letter "O" with the digit "zero", because they are right next to each other on the keyboard. Also, people tend to swap these on purpose in passwords. Ditto for the letter "E" swapped with the digit "three". And the letter "I" swapped with the digit "one". Also the letter "S" swapped with the digit "five". You might have made one of these common password character swaps when typing the initial password without even realizing it.

You cannot "bypass" encryption. That is the point.
Without the key that was used to encrypt the data in the first place, you simply have a drive full of meaningless 1's and 0's.

Suspect different encryption schemes maybe?