Do you have any idea why MultiBit can't open my wallet?
Sorry I don't know why, it sounds like a bug.
With password you mean the 12 wallet words?
Yes
How can I use my extended private key and a list of receiving addresses for my wallet to open my locked wallet? Can you explain this step-by-step?
Use the webpage I linked to in my earlier post. After you have entered your 12 wallet words into it and put m/0'/0 in the BIP32 Derivation Path box the page should automatically display the addresses in your multibit HD wallet together with their private keys.
You should be able to see them about half way down the page below the big heading that says "Derived Addresses".
If you know which address contains your Bitcoins you need to copy the private key shown next to that address.
If you don't know which address contains your Bitcoins then open the blockchain.info link below and starting at the top of the list search blockchain.info for each Bitcoin address in your list until you find the one containing your coins.
Don't let blockchain.info or anyone else know any of your private keys
https://blockchain.info/After you find which of your Bitcoin addresses contains your Bitcoins copy its private key, then follow these steps.
Download electrum 2.6.4 portable from here (because the latest 2.7 versions are buggy).
https://download.electrum.org/2.6.4/electrum-2.6.4-portable.exeCreate a new folder and copy electrum-2.6.4-portable.exe into it, then double click it to start the wallet.
An install wizard window should open. At the top of it select the "Restore a wallet or import keys" option, then click the "next" button.
Another window will open with a box in it that you can type your private key into.
After that click the "next" button and another series of windows should open. Leave each window's settings as they are and click the "next" button in each one until the wallet opens.
You can leave the password boxes blank, the electrum wallet can work without a password, and its password is not the same as your multibit wallet's password.
When the wallet opens it should sync within minutes and show your Bitcoins. You can use it to send them wherever you like.