the problem is not the blockchain. my wallet got corrupted after i restarted the QT client (it did NOT crash, it was shut down properly) and is not readable by the wallet anymore. I now tried five older versions, every time I start the client it tells me the wallet.dat is corrupted and not repairable. then wallet.dat gets renamed.
del all,use old version,old block chain,old wallet.dat.you'll get your coin back
again, I already tried that. The client can't load the old wallet.dat. even if you delete everything except for the wallet.dat, the client says that the wallet.dat is corrupted and can't be repaired. after that, the qt-wallet crashes...