I hope someone can help me. I have a bitcoin stored in a Bitcoin QT wallet from 2013 on my computer but have forgotten my passphrase. I entered my 17 word wallet recovery mnemonic on https://blockchain.info/wallet/forgot-password and it gave me a password which I may have used, however when I enter this in the Bitcoin QT wallet it does not unlock the wallet.

Is there a way of recovering the passphrase using this mnemonic?