You cannot use spaces.
A workgroup name set in [Workgroup Name] under [SMB Settings] is automatically used for [SMB
Workgroup Name], if any. A change to the workgroup name in [SMB Workgroup Name] is also applied to
[Workgroup Name] under [SMB Settings].
Perform a hard reset.
Click [Device Control], select [Hard Reset], and then click [Execute].
The settings are enabled after the hard reset is performed.
Selecting settings from the operation panel
You can also enable or disable the WINS settings from the setting menu of the operation panel.
Configuring SMB(P. 235)