While wanting to use DVD::Rip, Thoggen DVD Ripper and GnomeBaker to copy (or backup) a DVD today, I encountered the strange "Error trying to open: device or resource busy" on my Ubuntu box today.
I solved this by freeing the dvd drive from system access with:
sudo umount /dev/sr0
and everything worked. BTW:
For DVD .iso copies
I recommend GnomeBaker for easy copies...
Or see: How to copy a DVD to disk if you want a 1:1 decryption/extraction.