I guess there are quite a number of people now experiencing the same problem. I have to mention I have been using multibit 0.5.15 on a mac. I'd like some confirmation whether others are using the same version and system?

Like one of you I base64-decoded my keyfile, which gives me a Salted__kjncisiflsjfnlkasnetcetc output. This shows me that the keyfile has not been damaged during the time I had it on my computer. And that the problem lies before multibit's base64 encoding.

The fact is, the script is trying to emulate openssl AES 256 encoding, but it might be that it doesn't do that entirely correctly. At the same time it might actually be trying to decode it correctly, which results in an error. Although I still do not get the "AES key is wrong" error.

Another interesting thing I noticed is that the 0.5.15 version is not on github. I thought it was there before, I might be mistaken.