haos, you must delete your blockchain and re-download it again.
Save your wallet.dat and remove all files in the Romaing/PreminePlus Folder except wallet.dat. Then run the newest premineplus-qt Version 0.7.7.0.
Thanks. Redownloading the blockchain now.
Something bothers me: in the 0.7.5 wallet the sync was stuck at block 52165 (or something close to it) and under 0.7.7 the wallet show there is only 27370 blocks in the blockchain.
What happend here?