Anyway... have you tried using the openssl method to decrypt the .key file?
This command (on Linux, but you can also install openssl for Windows) will prompt you for the password and then decrypt the .key file (simply change the multibit.key part to match your .key file) and create the .txt file that contains the decrypted text:
This is my "key_test.key" file:
lB2dMrGBLdDyYxtiQ1GsyYg3CZkSDZZmvlVo7pnYIO3fGCTmc85d
This is what happens when I run the openssl command in linux:
This is the contents of newtest.txt:
If you're getting garbage output, it sounds like the .key file might be corrupt