The Seagate encryption algorithm works for files 4GB or smaller. It will however encrypt larger files but it will not decrypt them! How do I decrypt files larger than 4GB ? Seagate admits there is a problem but has no intention of fixing it because they no longer do business with the company that wrote the algorithm.

Sorry but there is no way to decrypt this without using the same algorithm. Also if you could locate the writer of the algorithm or someone else with similar programming expertise the algorithm could be worked upon.
sorry but it is most likely you have lost the decrypted information.
Merry Xmas

That posses a problem. They know there is a problem with the algorithm but don't plan to fix it. Wonderful. The problem is this, you would have to know what the algorithm was to be able to do anything about it and I doubt very seriously they are going to release that. That leaves you with the option of hiring a hacker to break the code or paying a specialty company to break the code and they are not cheap or well advertised. I can't think of any companies that do that work anymore. You are going to have to identify a Security company or the company that originally developed the Algorithm and see if you can work out a deal to get the corrected algorithm. The problem you have is your algorithm was designed for files smaller than 4gb and there is a permutation error that occurs on files that are larger. In a lot of cases this is a random fault that makes it very difficult to identify if not impossible depending on what level of encryption the algorithm actually represents. 32 or 64 bit encryption isn't so bad but 128 or higher is a real pain and expensive. There are some software packages available out there if you search the web for them, "Decryption Software", but again it is expensive and hard to find.