I think you can use the accelerator. I couldn't find your double spend in any block explorers, which means it's probably badly propagated.  The accelerator probably can't see the double spend either.

If you want me to try using the accelerator let me know.

Your wallet probably has a well known problem that's been discussed in numerous threads here. There's some solutions you can try in this quote. If you read through the threads in this board you will find more about the problem, and alternative solutions.

Yes, I forgot about that. If you leave the password blank when creating a wallet in 2.8 you get an unencrypted wallet file. I have been leaving the password fields blank in my personal wallets, so the change to whole wallet file encryption slipped my mind.

However, a bitcoin core wallet.dat is still in a completely different format to an electrum wallet.

It's possible. Every time I think it can't keep going up at this speed it goes up higher.

I didn't experience any of the previous mega rallies. Maybe that's why I keep thinking it's not sustainable for it to keep going up in value quickly. During the bear market every pump preceded a bigger crash. I haven't yet got used to every small crash preceding a bigger pump.

Did you only ever use one password for that wallet, or did you ever change it?

In 2013 if you added a password multibit classic made a timestamped backup in a folder whose name ends in -data. If you changed your password multibit classic made another timestamped backup. The first password would only work with the first timestamped backup, and the second password would only work with the second timestamped backup.

You said you had several rolling backups and a .key file. You can choose to manually create a .key file, but if you change your password multibit automatically creates one. If you ever changed your password then try all possible combinations of passwords and backups.

I think they want excessive KYC like ID cards scans, and video verification. Some users who can't provide it will lose their Bitcoins. Okcoin is also imposing a $1m annual limit. The whales won't be happy about that. A million dollars is small change to a whale. How can Chinese whales manipulate the price on Okcoin if they are only allowed to withdraw a million dollars a year?

http://www.coindesk.com/okcoin-huobi-move-end-chinas-bitcoin-withdrawal-freeze/

Search for the addresses from your multibit wallet in these block explorers. If none of the block explorers show they recently sent coins then your transactions probably weren't broadcast.

https://blockchain.info/

https://live.blockcypher.com/

https://www.blocktrail.com/BTC

If your transactions show as unconfirmed in those block explorers then try submitting the transaction IDs to this website exactly on the hour. If that website says successful then the viabtc mining pool will confirm your transactions in the next block it mines.

https://www.viabtc.com/tools/txaccelerator/

If your transactions weren't broadcast I suggest switching from using multibit classic to using electrum. Electrum can pay high enough fees to get fast confirmations.

There's instructions explaining how to switch to electrum without moving your coins at this link.

https://bitcointalk.org/index.php?topic=1922317.msg19181835#msg19181835

I would advise you not to use multibit classic because the network has so many unconfirmed transactions that multibi's highest fee isn't enough to get fast confirmations.

On OKCoin it's 16800 CNY. The Chinese are throwing money at Bitcoin on OKCoin now they are allowed to withdraw Bitcoins again.

Can you find a file called decoded.key after you run the quoted command? If you can find it, and open it in notepad it should look like the example HCP posted.

If you can't find decoded.key then try this command instead of the one you were using, but swap 111111111111111 for your password.

openssl enc -d -aes-256-cbc -a -in my_private_key.key -pass pass:111111111111111 > decoded.key

If a file called decoded.key appears in the openssl folder after you run it then it worked.

Submit your transaction's ID to this website on the hour every hour until it says acceleration succeeded. Afterwards the viabtc mining pool will confirm your transaction in the next block it mines.

https://www.viabtc.com/tools/txaccelerator/

There are only 100 free slots an hour, and they are in demand. To stand a chance of getting accepted you have to submit your transaction exactly on the hour, not a few seconds later.

No electrum uses a comopletely different wallet file format to Bitcoin core. If you open a core wallet.dat in a text editor it appears as random characters. If you open an electrum wallet file in a text editor it's human readable.

Click file, then receiving addresses. Find the address you sent coins to in the window that opens, right click it, and select copy address. Close the addresses window.

Click help, then debug window.

In the debug window that opens click console.

In the text box at the bottom of the window type

dumpprivkey yourAddress

where yourAddress is the address you sent coins to and copied earlier.

Press your enter key.

The private key for that address should appear in the console window. Copy it.

This is an example private key.

L48toSntMVhC2az4KAQCWscrQGfPbT55yCgzM5cmx9Ao69pTdwrq

Download and install electrum.

https://electrum.org/#download

Import your private key into it using these instructions.

http://docs.electrum.org/en/latest/faq.html#can-i-import-private-keys-from-other-bitcoin-clients

Afterwards your coins should be spendable.

Did your old wallet consist of a bunch of .py files?

You can find the wallet releases made in 2013 at these links.

https://github.com/spesmilo/electrum/releases?after=1.6.0

https://github.com/spesmilo/electrum/releases?after=1.7.3

https://github.com/spesmilo/electrum/releases?after=1.9.5

https://github.com/spesmilo/electrum/releases?after=2.0b3

They don't have an executable installer like today's wallets. They are just some .py files. You could try downloading one from a likely date, running it, and trying to import your seed words into it.

Was your wallet.dat file encrypted (was it password protected)?

How old was the bitcoin software you used to generate it? The database it uses changed from one type to another years ago. During 2013 it changed from using Berkeley DB to LevelDB.

When you say the "original bitcoin wallet program" do you mean the first ever bitcoin software released by satoshi?

I have the original bitcoin wallet program, which was version 0.1.0

I tested generating three different wallet.dat files with it, and opening them in a hex editor. The results are below. They all begin with this sequence of bytes "00 00 00 00 01 00 00 00 00 00 00 00 62 31 05 00 09 00 00 00 00 20". If you search your hard drive for that sequence you might locate an old wallet file.

I don't know, it depends how many unconfirmed transactions there are in the network. There's been a huge backlog for weeks. It was starting to go down, but its started going up again today. There are currently over 90000 unconfirmed transactions in the network.

https://blockchain.info/unconfirmed-transactions

This website currently recommends paying 420 satoshis/byte for fast confirmations. but your low fee transaction only pays a fee rate of 76 satoshis/byte.

https://bitcoinfees.21.co/

A few months ago the network would either have confirmed it or forgotten it within three days. However, recently people have been complaining that the network hasn't forgotten their low fee transactions after three weeks because some nodes keep rebroadcasting them.

If you do nothing you might get lucky, or might possibly have to wait weeks.

I'll try the viabtc accelerator again on the next hour.

edit

I tried, but was unlucky again. I got a "Submissions are beyond limit. Please try later." message.

edit2

I successfully submitted your transaction to viabtc's accelerator. The viabtc pool will confirm it in the next block it mines if no other pool confirms it. It normally mines a few blocks a day, so it should be confirmed by this time tomorrow. There's a list of viabtc's latest mined block times here.

https://blockchain.info/blocks/ViaBTC

edit3

ViaBTC confirmed your transaction when it mined block 468956. It's now got 12 confirmations.

I can't advise you how to make a child pays for parent transaction in core because I don't have enough experience.

An alternative you might try is contacting either quickseller or macbook-air, and asking them if they will confirm your transaction for a fee.

They both have access to f2pool, which confirm your transaction.

You can contact them by clicking these links. However, they are probably overloaded with requests to confirm transactions, so might not reply.

https://bitcointalk.org/index.php?action=pm;sa=send;u=358020

https://bitcointalk.org/index.php?action=pm;sa=send;u=16114

They charged 0.0001 BTC per transaction last year, but probably want a lot more now.

If you saved your wallet files to a storage device like your computer's hard drive, or a flash drive then you could use software called pywallet to scan the drive for private keys. This is the pywallet thread.

https://bitcointalk.org/index.php?topic=34028.0

If you control the address the coins are being sent to then you might be able to do a child pays for parent transaction. Is 1BgYCcho6KgCnQBYA4qh1gDbzgyFivqhXE  an address you control?

Achow101 explains child pays for parent transactions in this quote from the linked thread. Unfortunately I don't have enough experience of using core to advise you about them, but I'm sure other users with more experience will help.

https://bitcointalk.org/index.php?topic=1802212.0

The problem is that there's two transactions in the double spend, one with a high fee, and the other with a low fee. Unfortunately most nodes and block explorers can only see the one with the low fee. Luckily the viabtc transaction accelerator can only see the low fee transaction. That means if you can get it to accept it the viabtc mining pool will confirm it in the next block it mines.

The viabtc accelerator only accepts 100 transactions an hour and it's overloaded. If you submit your transaction ID to it exactly on the hour it might accept it. I just tried but I was too late, all the available slots had been taken a few seconds after the hour.

Try submitting this transaction ID to it on the hour 3eb102f7273c983e0fd52567da7ca41e3ef66a232f7d611ce563989376d78115

This is the link to the accelerator.

https://www.viabtc.com/tools/txaccelerator/

Maybe someone else can suggest a better solution. I'm not very experienced at using core.

If you wait long enough one of the transactions will confirm. They both send coins to the same address, so that address will receive the coins sooner or later.