First you have to unarchive it. There should be a button for that there.
To clarify is address "1DT2ttQ7kxBiPZngRyXcwodKjZ8Q6oxCgG" an imported address or a part of your HD wallet in blockchain.info?
If its part of your HD wallet in blockchain.info you can use your seed for the following:
I've successfully run an electrum wallet in the same system (Win7 - 32bit) before but I can't remember which version is it. I suggest running a standalone executable first and try the previous versions if it doesn't work. Import your wallet using your backup phrase in electrum. Just be sure to tick the
BIP 39 Box in
Options when electrum prompts you to enter your seed. After that you can sign a message.
You can also use mycelium which is a android/ios wallet or any wallet that supports importing. Here's a tutorial for that:
http://bl4nkcode.info/bitcoin/how_to_export_blockchain_wallet_private_key
If its an imported address, After you unarchive it you'll find your address in the
Imported Addresses tab. Click the
More Options --> Private Key.
And you can now import it to electrum (desktop), mycelium (Android), coinomi (Android) etc.