Hello, my Blackcoin wallet was working OK since this morning when I openned it again. I receive this error on start and then program crashes. Anybody can help me? I'm using W7 64 bits

Thanks. I already tried this and the error persists.
You might wanna try backing up your wallet, then delete everything in your %appdata%/blackcoin folder except the wallet.dat, then run the blackcoin-qt.exe again. That may work, but can be risky so do it at your own risk.
I have done this 2 times without any problems, so I'd say its not risky as long as you DONT delete wallet.dat and of course always keep backups of it on other places.
Then the wallet will redownload the blockchain, so it takes time.