You should completely rename the .bitcoin hidden directory in your home, then start up Bitcoin-Qt. Bitcoin then should make a new .bitcoin directory with a blank wallet and start downloading the blockchain. If this works, then close Bitcoin and put your backup wallet.dat in that directory. If you get the error again, your wallet file is corrupted.
You can attempt to recover the wallet.dat file in-place by starting bitcoin-qt with the -salvagewallet command-line option, but it would be better to locate an uncorrupted wallet backup.
Thank you.
Actually Im working on a dedicated server with ubuntu.
I moved the .bitcoin folder and and reinstalled bitcoind (with --purge).Now I'm not getting any errors.But I have to waith until it synchs.
I will let you know.Im affraid my wallet is corrupted anyway...
But first of all, THANK YOU.