Hello, do you have 90GB free disk space on the disk you are trying to encrypt the folder on?
If you do, can you instead of this big folder, try to protect one smaller folder, just for test?
If that works, do you have an external disk with 90GB free? If you do, please try to copy that big folder over to external disk, and then try to protect that folder, as target folder for the disk image you can select either the same external disk or your internal one, up to you.
If that encryption finishes well, then let me know and we will move the things so that you end up as you wanted initially.
Rgds
Zsolt