If it came with Cubase 6 then it could still be HalionOne SE content which is a different story. If I remember correctly HalionOne SE was included even when Halion Sonic SE was introduced so users can still access older sounds on legacy projects.
(Just dug out my old Cubase 6 disk and confirmed this.)
The fact that some Halion Sonic SE sounds can be opened in Halion 5, but not edited, is why I’m thinking of the license. These hsb files might be locked or just plain incompatible.
I tried registering that exact same file now and got the same message.