I've followed this guide a few time to succesfully offline sign transactions and then broadcast them from another computer.
However, now that I try I get an "Invalid Signature" error when attempting to broadcast from blockchain.info/pushtx . I've also tried broadcasting the same TX from Electrum and get error code 25.
I tried twice with no luck.
Any ideas?
try doing with brainwallet offline
I did as in OP's guide which is using Brainwallet.org offline to sign a transaction.