Looks like a corrupt wallet.dat? If you have another backup of the wallet, try that file. You could also try and start the client with a new wallet.dat (move the old wallet and let it generate a new one), let it load, stop it and try the old wallet.dat again. Or, start up with a new wallet and try the 'import wallet' function from the console.
No experience with py here, unfortunately, but I don't think that would work with an encrypted wallet anyway.
Thank you for your help.
I have another backup but with the same error.
I just tried the import function. I'm just a little confused if it is the same command as in bitcoin client. I've tried "help importwallet" to understand, but the command showed is importwallet "filename". I've tried to create a wallet1.dat and then:
importwallet "wallet1.dat"
It returns the following:
Cannot open wallet dump file (code -8)
Am I doing something wrong?
Also, make some copies of your left over back up, just in case in the process this one gets fried as well.