This is one of those annoyances which seems to be giving lots of Ubuntu users grief! Luckily there's a simple fix for this...
Using console/terminal type in
sudo nano /etc/samba/samba.conf
to open the file you need to edit in the nano text editor
once it's open you'll see a whole load of lines of instructions. Look at the section starting with the line [global] and add to the end of it the following lines exactly as shown here:
client lanman auth = Yes
client ntlmv2 auth = no
then save your file and reboot the PC.
Your password protected shares should now work as they should do.
Our thanks to
Trab for the fix.