Quote from: AlexanderScott on September 12, 2016, 02:19:10 AM

The person that helps the most in getting me my bitcoins back will get 1 bitcoin reward.

I have a wallet in Bitcoin core.
I think I upgraded to core 12.1 maybe 9 months ago, and my wallet is older than that.

0.12.1 was not released 9 months ago. It's much newer than that.

Quote from: AlexanderScott on September 12, 2016, 02:19:10 AM

I haven't used core very much, but decided to receive bitcoins to core wallet some time ago, which of course I expected to work.

I know I know, I shouldn't have used a wallet that didn't have the 12 words that will keep my private keys forever, but I knew that I had multiple backups of the wallet so I thought it couldn't be that risky to use Bitcoin Core.

However, now my core wallet doesn't work. I's saying that the password is wrong. I don't remember changing the password, and why would I do that anyway, because I had a nice system on it. But I cannot sign messages or send the bitcoins. It's as if the wallet file is corrupted or something, and now I cannot unlock the private keys. I've tried all kinds of password, but they don't work. The original password I set on the wallet is not working.

Are you sure you are using the correct wallet file? Is the correct file in the correct data directory?

Quote from: AlexanderScott on September 12, 2016, 02:19:10 AM

If I didn't know any better, I'd suggest that Core has changed the way it stores or retrieves the private keys in a way that's not working properly with the old way the keys were stored. So after upgrading maybe the new keys are not compatible with the wallet? I don't know.

No, nothing of that sort has changed.

Quote from: AlexanderScott on September 12, 2016, 02:19:10 AM

I have backup of the core wallet with a known password that can sign messages, but when I use those wallets, they don't generate the same bitcoin addresses.

I thought even core stored at least 100 addresses in the wallet file, but it seems these addresses are all generated on the spot, with no memory of what's happened before and no seed for the random generator.

No, you're wrong. Bitcoin Core does pregenerate 100 addresses and those are in fact stored in the wallet file.

Quote from: AlexanderScott on September 12, 2016, 02:19:10 AM

Joke aside, I know there's a guy in the bitcoin community that helps people with these kinds of things, and he has a reputation for doing a good job and being an honest person. I don't remember his name. Anyone know who I'm talking about?

Dave at wallet recovery services? If that's who you are thinking of (he brute forces wallets), he probably can't help if you have no idea what the password is.

I highly suspect that you either have the wrong wallet.dat file or the wrong data directory. Go to Help > Debug Window and look at the line labeled Datadir. Does it show you the data directory that you have been putting wallet files into?