If you allow your users to define a personal encryption key for their files, you must have the key available to decrypt the files you are restoring. If you cannot provide that key, neither you nor Mozy can decrypt your files.
If you do need to decrypt your files, your restore experience will be better if you start by putting all your restored files into a temporary folder, perhaps on your desktop. Then you can decrypt using your personal key, and in that process put your files into their final destination.
If you are not sure whether you chose personal encryption, try to open a file that you just restored to your computer. Any text file (with the .txt extension) is probably a good choice for this test. If you cannot open the file and if you see any messaging about encoding or encryption, your files were encrypted with your personal key.