Yes, that's the risk of encryption: losing the encryption key and so losing all your data. That's why our standard advice is to always keep an unencrypted copy on a safe place (two safe places is even better).
I'm afraid that only the maker can help you. If they don't, contact www.lostpassword.com and ask for a quote. My guess is they will ask you to send them the disk.
If it's just the data you can't find, and not the key, see their page about "Backin up Chrystainer vaults" on http://www.cypherix.com/cryptainerle/online_help/index.html
It tells where to find the file in Windows 98, 2000 and XP.
My laptop is defunct but I have salvaged the hard drive intact. After reinstalling cryptainer on my new laptop I need to find the cryptainer volume on my old hard drive. This seems to be a hidden folder which I cant locate. I have mailed Cypherix but have not received a reply and there is nothing on the website to help. Can anyone help?