I fixed some days ago my somehow corrupted and completely non working wallet on MAC OSX by downloading the latest version again ;
backup your wallet.dat , it is in /Users/»Your Username«/Library/Application Support/MintCoin/ before you fiddle around .

• I renamed my MintCoin Folder appending to its name anything ,
  
• installed the latest wallet app version anew , started it up ,
  and quit it while it was starting to resynch the blockchain from scratch .
• At that point , the MintCoin Folder was recreated anew and I only had to
  drop the contents in Bootstrap.dat into that fresh MintCoin Folder …
  - it took the Wallet only a few minutes to synch up fully to the last few transactions on the public blockchain .
• Lastly , drop the latest backup of your wallet.dat into the new MintCoin folder and you are good to Ball .