I know this is an old post, but I haven't been able to be around much in a while.
I have used AxCrypt before for people that felt they needed an extra level of security. can encrypt files and/or folders. nice and free
the only time I ran into an issue was a user had encrypted their tax documents folder at home on the laptop. got to work and could not decrypt the folder. she had the right password, it just wouldn't decrypt it. talked to the company, they said SOL no back door. I got to asking questions and turns out at home she was using a full size USB keyboard. I went and got one plugged it in and it worked. I played with it some. If I encrypted it with the laptop keyborad the USB could decrypt it, but not the other way around.