I have played many other DVDs on my pc with Kaffeine or VLC but now neither of these programs recognise the specific DVD that I want to play.

When I start up Kaffeine, I get an immediate error:
"Access denied to /media/cdrom0"

A friend of mine made this DVD for me and it works absolutely fine on her PC. She also uses Ubuntu and ran the DVD in Kaffeine.

Any suggestions?