A machine account, typically stored in /etc/passwd, takes the form of the machine name with a “$” appended. Some BSD systems will not create a user with a “$” in the name. Recent versions of FreeBSD have removed this limitation, but older releases are still in common use.

The problem is only in the program used to make the entry. Once made, it works perfectly. Create a user without the “$”. Then use vipw to edit the entry, adding the “$”. Or create the whole entry with vipw if you like; make sure you use a unique user login ID.