Open index.html, select the transactions tab, and paste in your blockchain.info private key. See what the balance is after you click ok to downloading the transaction history.
I looked up that TXID and the to: address, and that amount never transferred, so it should still be at the original key.
I did some digging and I believe this is the tx that messed everything up:
Jan. 4, 2013, 4:21 p.m. b42feaa04c141700f7c154f4ac1c604173cc4ee38e9fd4cbe0210bd7e764435a This transaction includes 0.00100000 BTC as fee. size: 978 bytes priority: 3,253,465,754 input: 19.10148815 BTC
0.01899999 BTC from 73300f82c5556ed983ac2d66f1e3a7d537cbc374a4d3925332cc09b96a848143:1 (13h1DP2Boo9TAsenphroACxhNy7pGxDYXd)
2.60000000 BTC from unconfirmed c4f5568a7fa4e9f44b0978e5309f774128704c55616600ea9bd2e3c35aa73d06:0 (1dice97ECuByXAvqXpaYzSaQuPVvrtmz6)
0.76905998 BTC from 6ac72ed035287ce7ad661043718c16488c46d2bea53ef5e231054d2763d1813d:1 (14719bzrTyMvEPcr7ouv9R8utncL9fKJyf)
0.58750666 BTC from d3ef9ec507aa44d9864116049deef554f91ba0e08b347e14e020f9b2e4a53e78:1 (13h1DP2Boo9TAsenphroACxhNy7pGxDYXd)
15.12592152 BTC from 19180ff37d0c1347b6fce4cb3591b3f5818c12b4ab6eefafe813f87053c9d0ed:1 (1Bd5wrFxHYRkk4UCFttcPNMYzqJnQKfXUE)
output: 19.10048815 BTC
5.08770000 BTC to 1Enb1nB17S2vysY68kQLUwUuHk9jyF5vD6
14.01278815 BTC to 1HjDauL2kth6KJUz5vX198Nvp1xN1hgYRb