Hello. Glad to help.
This can happen if the disc has been put in upside down accidentally, if both sides are highly reflective (e.g. blank recording discs). If so, you need to get the system to eject the system before it attempts (and fails) to read the wrong side of the disc:
On the back of the Acoustimass module (sub woofer) is a power switch. Use this to the turn the system off and wait 30 seconds. Switch it back on, the media centre flashes up "Bose 321" - press the eject button firmly once as soon as this disappears. If this works, contact Bose with the serial number from the media centre to see if the system needs a (free) software update (a disc they send in the post) - just in case the system is having general disc reading issues.
Turn the box over and there are 6 screws holding the top on. Unscrew all of them.
Gently pull the top of the box off, you will see a small form factor motherboard under a tv capture card and next to the dvd drive. Remove the tv capture card
and unplug it from the motherboard. Gently pull the front of the dvd case open to unseat it from the drive (this takes patience and a soft touch).
Remove the front panel of the bose system by gently prying it apart
lift up the DVD drive (its a 5 1/4" drive like is in your computer).
On the front of the drive is a small pinhole. Take a paper clip and shove it in there. This will trigger the manual release for your dvd player.
Take out the dvd and put it all back together.
This should solve it.