US DVDs are in NTSC format, while European DVDs use PAL format.
Not only are there region locks, but resolution and framerates are bit different.
US DVD is 720x480 at 29.97 FPS
PAL DVD is 720x576 at 25FPS.
Im not entirely sure if changing the region would help, never tried it, but I doubt it.
But I do know these are the differences that may pose a issue for the player itself.
There are however, 2 options to work around it, if all else fails.
One is to watch it on the PC. PC should not have a problem playing either or. In this case, a region change should work.
Or, if they know anything about video encoding, copy the disc to thier PC.
Then, convert it to PAL format (with something like Nero for example) and burn to a DVD so it can be played in a home player.
So long as you have the original copy of the disc,and its only for personal use, you should be OK going this route.