getrawtransaction error? [Code -5]
Since bitcoind/Bitcoin-qt 0.8, no transaction index is kept anymore by default, as it is not necessary for validation in the new database model.

Instead, there is only a database of unspent transaction outputs, which has enough information to (slowly) locate transactions in block files. getrawtransaction uses this, but it only works for transactions that are not yet spent in the block chain.

If you want to be able to look up historical transactions, you need to set the txindex=1 configuration option (or start with the -txindex command line flag). As this setting can only be set when the database is created, you'll need to rebuild it from scratch (using -reindex).