There are quite a number of threads about this in
the MultiBit subforum...
If you are using MultiBit HD, the "Password did not unlock the wallet" is a known issue, which I believe is related to MBHD using a slightly older version of the BitcoinJ library. The newer library is including a "version" field when calculating the transaction hash. The older version does not, so when it calculates the tx hash it comes up with a different value and freaks out thinking that it hasn't decoded the wallet correctly.
Anyway, there are a number of "solutions" that will get you access to your coins until the MBHD devs release a fix.
1. The quick and easy solution, assuming you have an Android or iOS device, is to install "Breadwallet". It is compatible with MBHD seeds. You can restore your wallet using the seed words, wait for it to sync and your transactions and balance should show up. (Note: on Android, Breadwallet requires a relatively new device. If it doesn't work, try
"Simple Bitcoin Wallet")
Note: at this time, these are the only two wallets that are known to use the same BIP32 Derivation Path as MBHD.
2. If you can't use Breadwallet (or Simple Bitcoin Wallet),
I have written some python scripts that can extract the private keys that contain unspent coins (UTXOs) from your MBHD wallet file. You can then sweep (or import) those keys into the wallet of your choice. I'd recommend Electrum.
3. If you are unable to setup and/or run Python scripts, you can find your coins manually by creating an offline version of:
https://iancoleman.github.io/bip39/Put your mnemonic seed in. Under "Derivation Path" section, click on BIP32. Select "MultiBit HD" from the "Client" dropdown (derivation path should show as m/0'/0). All your generated "Receive" addresses and matching private keys should show at the bottom. Depending on how many transactions/addresses you've used, you may need to keep clicking "Show more" to generate more addresses/keys. Make a list of all the private keys.
You can check which addresses have coins by putting them into a blockexplorer... NOTE: DO NOT put the private keys into a blockexplorer!
Once you've gone through as many receive addresses as you think necessary to cover all your received coins, you'll need to select "Custom" from the "Client" dropdown, and set the derivation path to m/0'/1. This will then show you all your generated "Change" addresses and matching private keys. Again, you may need to click "Show More" depending on how many transactions you've made. Add all these private keys to your list.
Once you think you've got enough (Maybe 100 Receive + 100 Change private keys... depending on the number of transactions you made)... you can then sweep or (import) those Private Keys into a wallet of your choosing. Again, I would recommend you use Electrum.
NOTE: If you don't find all your coins, you need to keep generating addresses using the BIP39 Tool... and sweeping/importing them until you find them all.