I have been using the chat log encryption feature on my home computer as a just-in-case method of protecting some sensitive business conversations. These encrypted files were looked at fairly regularly by me to check on some important information. However, recently I have not been able to check these files, as the encryption password has changed. I am not sure how this has happened, as very few people have access to my computer, and my password (which to my knowledge no one else knows) would have to be known in order to change the encryption password. Currently I have disabled encryption for all new conversations, but this does not change the fact that I am locked out of some important files and I have not been able to find any way to access them. Is there any way to disable the encryption on these files now? This is a matter of fairly high importance, so any advice offered would be much appreciated.

When you disable encryption and then re-enable it, Plus should ask if you want to re-encrypt your logs, try it.
However, I think there's a bug with this (I think Patchou said he was gonna check it).