simplewallet shows the following error,
& at the same time bitmonerod shows the following,
Transaction with id= <523cba83de2a2634fb113c0066550c8925d261bed4762fba5fa841bf5a57b6e8> used already spent key images
2014-Jun-26 10:11:24.856020 [RPC0]Transaction verification failed: <523cba83de2a2634fb113c0066550c8925d261bed4762fba5fa841bf5a57b6e8>
2014-Jun-26 10:11:24.860020 [RPC0][on_send_raw_tx]: Failed to process tx
I have 20 XMR balance & just tried to send 5 XMR!
Delete poolstate.bin from %AppData%\bitmonero (win) or .bitmonero (linux). Backup your wallet (the .keys file). Delete the wallet.bin file. Start your wallet as usual and the .bin file will be recreated based on the .keys. Refresh the wallet and try to send the transaction again.