To fix this issue:
1. Close your wallet
2. Go to your aircoin app data folder (type %appdata%\aircoin after pressing Windows + R)
3. Locate and delete the files blk0001.dat and blkindex.dat (Make a backup of them first just in case)
4. WARNING: DO NOT DELETE YOUR WALLET.DAT FILE! Its always recommended to make a backup of it.
5. Reopen the wallet, and it should sync perfectly
Don't know, I'm trying to figure it out.
But I assume it can be because of some stuck POS blocks, this can happen when too many coins are in one place.
They should be fixing and will be available again shortly, they just need to resync the blockchain.