First, There is one thing that confuses just about everyone because it's not documented well. There are two methods of using samba to share directories in Ubuntu and you are using both on the same target:
One is Nautilus-share:
The other is Classic-share:
They are configured differently so I would suggest you get rid of the Nautilus-share version. Just go back into Nautilus and reverse the steps you used to create the share.
path = /home/paul/Desktop/MacShare
valid users = paul
read only = No
Second, In your classic share you have:
Did you create a samba password for user "paul"?
Third , I don't know where this is coming from but this is the second time in as many days that I've seen this line in smb.conf:
sudo smbpasswd -a paul
You will need to comment out that line and restart samba:
username map = /etc/samba/smbusers
Open Terminal and type:
Find the "username map" line and place a # sign in front of it so it reads:
gksu gedit /etc/samba/smb.conf
Save the file, exit gedit, and back in the terminal restart samba:
#username map = /etc/samba/smbusers
Forth, this is the wrong syntax:
sudo restart smbd
sudo restart nmbd
It should be:
Oh and keep the Ubuntu firewall disabled for the time being - at least until we can get an actual connection.