What version of windows is encrypted with bitlocker and what version are you running encase on and trying to decrypt it with?
MS bought out a new encryption scheme XTS-AES with one of the updates to Windows 10 [version 1511]. Any version of windows previous to this will not be able to decrypt.
So, as an example, if he is running Anniversary or a Creators update of windows 10 when he encrypted the drive and you are running encase on windows 7 (which is still what guidance software recommends) then you won't be able to decrypt even with the correct recovery key.
You're a Rock Star Amne5ia! I moved the case over to a laptop that is running Windows 10 and EnCase 8.04, used the PDE to mount the volume and the credentials are now recognized.
I can't thank you enough for helping me step back from the forest to see the trees.
AmNe5iA,
Your advice just allowed me to decrypt seven laptop images to my great relief.
Please PM me with your physical mailing address as I would like to send you a small gift as thanks.
I understand your advice was given here without any expectation of remuneration, but it was extremely valuable to me and my practice.
The newest version of dislocker has support for this as well, I'm quoting these from their GitHub site
Windows Vista, 7, 8, 8.1 and 10 encrypted partitions - that's AES-CBC, AES-XTS, 128 or 256 bits, with or without the Elephant diffuser, encrypted partitions;
BitLocker-To-Go encrypted partitions - that's USB/FAT32 partitions.