fail to set machine ownership

[dingding]

i create a automatic pool with automatic assignment unchecked, after pool created, i manually assign user to a desktop, but it failed, error message is as below:

server error: fail to set machine ownership for ......

so i enable auto assign for this pool, and login from view client with the user previously failed to assign to the desktop, it succeed.

and the user is assgined to the desktop now.

anybody know the cause?

also i want to know the usecase when we use manual assignment.