The error would indicate that the node you're attempting to broadcast your transaction through, still thinks that the UTXO is already being spent in an unconfirmed transaction.

It's possible that it's either on your local node, or a node that your Bitcoin Core is attached to... Note that it may not necessarily show up on any given block explorer, so I'd recommend checking a number of different block explorers to see if that original transaction is still floating around:

https://www.blockchain.com/explorer
https://btc.com/
https://blockchair.com/bitcoin/
https://live.blockcypher.com/btc/
https://blockstream.info/

The bolded part might your issue as I think that the armory doesn't work without the internet it needs to be sync and bitcoin core must be fully synced to make the armory work.

But you can still get the raw transaction and broadcast/push them manually to any of these below.

- https://coinb.in/#broadcast
- https://blockchain.com/btc/pushtx
- https://blockchair.com/broadcast

but i deleted bitcoin core mempool.dat?

what does zapwallettxes do?

It seems that it needs to put -zapwallettxes under the bitcoin-qt shortcut to make it work and it's a solution for stuck transaction.
I don't know if it will work but worth trying.

I found something on google there are two options on achow's blog that you can follow including this -zapwallettxes and abandontransaction
You can read it from here https://achow101.com/2016/07/Bitcoin-Core-Troubleshooting

zapwallettxes should only remove transactions in the Bitcoin Core "wallet.dat" itself... this "offline" transaction was sent from Armory via RPC. So it wouldn't be recorded in the Bitcoin Core wallet.dat, so there would be nothing to "zap". Theoretically, deleting mempool.dat should have removed this transaction from Bitcoin Core.

It's possible there is something screwy with the Armory databases that the "rebuild and rescan" did not fix. While drastic, and requiring a bit of time to rebuild, you might want to try the "Factory Reset" option in Armory and select the "also delete the databases and rebuild" option:


Then shut down Armory and restart it. That should hopefully purge everything and let you broadcast your transaction.

NOTE: Make sure you have a wallet backup before you start!

Probably worked together with 'deleting the mempool.dat file' since it also contains that transaction.

---

I know this is late but if it's just an issue with a single unconfirmed transaction,
a simpler solution is to create a signed transaction that can be broadcast outside of Armory.

After using "Clear Unconfirmed", create the same txn using the cold-storage method but instead of using Armory to broadcast, just copy the the "RAW TX (HEX)"
and broadcast it using an online service like: https://live.blockcypher.com/btc/pushtx/ or https://blockstream.info/tx/push

If you don't know how to get the Signed Raw Tx, follow this:

• Click "Send", fill up the transaction info: fee, recipient, amount, etc.
• On the same window, check "Create Unsigned", then click "Continue"
• On the next window, click "Copy to Clipboard", then "Continue"
• Next, paste the copied text, click "Sign", "Continue" then type your password
• Click "Copy Raw Tx (Hex)".
• Lastly, go to an online push service, paste and send that signed RAW tx.

After getting one confirmation, the conflicting transaction in your Bitcoin core's mempool or wallet.dat will be dropped.

Armory uses core to broadcast transactions.
When there is no internet connection, armory still tries to broadcast it using core. Core just isn't able to forward it into the network.

So it kinda has to be somewhere "stored" by core, i'd say.

Since the tx went through the RPC, Core can correctly assume this tx is yours. I don't know why it would keep track of it, and somehow I doubt zapwallettxes has an actual effect in this case. I'm going to guess Achow only suggested to use this CLI arg as part of a the standard procedure to clean up stuck transactions in Core's Wallet. Armory isn't related to Core's wallet, it only makes use of the networking and consensus parts.