Recently I wanted to play a DVD on my Linux laptop, and had the following messages in dmesg:
sr 8:0:0:0: [sr1] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE sr 8:0:0:0: [sr1] tag#0 Sense Key : Illegal Request [current] sr 8:0:0:0: [sr1] tag#0 Add. Sense: Read of scrambled sector without authentication sr 8:0:0:0: [sr1] tag#0 CDB: Read(10) 28 00 00 00 13 d5 00 00 01 00 print_req_error: I/O error, dev sr1, sector 20308 Buffer I/O error on dev sr1, logical block 5077, async page read
The solution was to install libdvdcss2, which is unfortunately not directly available in the Debian repositories. Instead, I had to install an installer for it:
$ apt install libdvd-pkg $dpkg-reconfigure libdvd-pkg
Source: Ubuntu help: Playing DVDs.