After import some of the transactions show n/a as address. What does this mean ?
After "import"? Do you mean after restoring the wallet.dat, or, are you actually importing -- i.e., trying to use pywallet or something to manually import the keys from the old wallet?
Also, you might try -upgradewallet, perhaps if there is a data corruption problem that the upgrade to the current format will resolve it?
But, make sure to not delete or overwrite your backup from six months ago, just in case.