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Do you have a firewall running on the computer?
Since you copied over the smb.conf I don't think its a matter of WORKGROUPS not being setup properly. Double check the setup of the workgroups and make sure they match on all machines.
Also, you must restart the samba service if you make changes to smb.conf
## Browsing/Identification ###
# Change this to the workgroup/NT-domain name your Samba server will part of
workgroup = WORKGROUP
sudo service smbd restart