It seems like many people run into this issue. You were on the wrong fork so you upgraded to 0.8.54 and now your client doesn't sync. It seems to me that the issue is that your client was still syncing after block 607, so now you have the wrong blockchain.
It's easy to fix this issue:
1. Backup your wallet! I don't want you to risk losing any coins.
2. Close your client
3. Go to C:\Users\<your user>\AppData\Roaming\MemoryCoin in Windows or I believe ~/.memorycoin in Linux
4. Delete everything but wallet.dat and peers.dat
5. Open your client, it will download the new blockchain and it will sync