This has been bugging me for days until I found this solution:
http://www.jordanpeterson.me/node/222 Ubuntu 9.10 does not allow folder sharing.
Right click on the desktop, select "Create Folder", type a name, hit the Enter key.
Right click your named folder, and select "Sharing Options".
Up comes a Folder Sharing Window, checkbox "Share this folder" and "Allow others to create and delete files in this folder", then click "Create Share".
You may get an error like:
failed to execute child process "testparm" (No such file or directory)
Open up a terminal window by clicking "Applications" dropdown menu of your Desktop, then "Accessories", then "Terminal". This is often how we fix things like this. Type the following or highlight and within the terminal window push both mouse buttons down:
Try Approach A first: sudo apt-get upgrade
... and if that doesn't do it for ya, try Approach B:
sudo cp /usr/bin/testparm.samba3 /usr/bin/testparm
sudo cp /usr/bin/net.samba3 /usr/bin/net
sudo chmod +x /usr/bin/testparm /usr/bin/net
Try creating the share again.
Huge thank you to Jordan Peterson for posting the fix and stopping me tearing my hair out!