Hi,
I'm afraid that if Messenger Plus! says it was the wrong password, that it realy was the wrong password you've typed. Or, that you have misstyped the password when you've set it up. The password wont change on its own, that's impossible. Also filtering on contacts have no influence what-so-ever on the encryption.
What could have happened is that your logs became corrupt because of a small (otherwise hidden) hard disk failure or something. If that is the case, then it would be possible, at least in theory, that Plus! will say that your password is wrong while it was the correct password. But in practice that is very unrealistic (because for that to happen, the corruption needs to be very specific on certain areas of the encrypted log file). Normally, Plus! would say that the logs are corrupt if they were, so....
Anyways, unfortunatly, there is no way to decrypt logs if you do not know the correct password. There is no 'backdoor', 'trick', 'master password' or whatever else...
Try any combination you can thing of, lowercased and uppercased letters. Also try certain different keys which are next to the ones you thought were the correct ones (eg: q instead of w (on a qwerty keyboard)), etc...
As a last resort you might wanna check if you haven't also enabled Windows Live Messenger's own chat logging. If so, there might be a chance that the logs are saved (unencrypted) by Messenger...
So, I hate to say it but if you can't produce the correct password, you're logs are lost I'm afraid.
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