[Samba] string_to_sid: SID <username> is not in a valid format

[Frostyfrog]

I'm not quite sure why this is happening, I used to be able to connect
perfectly fine to my share. Then I updated and rebooted and now I'm greeted
with this message, and a login prompt where my credentials are never
accepted.

[http]
  comment = HTTPD Server
  path = /srv/http
  writable = no
  public = no
  browsable = no
  valid users = frostyfrog
  write list = frostyfrog
  force user = http
  force group = http

# smbd -i -d3
<snip>
get_referred_path: |http| in dfs path \X.X.X.X\http is not a dfs root.
Allowed connection from X.X.X.X (X.X.X.X)
string_to_sid: SID frostyfrog is not in a valid format
Forcing Primary Group to 'Domain Users' for frostyfrog
Forcing Primary Group to 'Domain Users' for http
Forced user http
Forced group http
Connect path is '/srv/http' for service [http]
string_to_sid: SID frostyfrog is not in a valid format
Forcing Primary Group to 'Domain Users' for frostyfrog