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.