Set Top Player Not Playing Some Burned DVD's

My grandmother recently received two DVD's from Germany of some relative's wedding.  However, they would not play in her DVD player.  So, since my parents are somehow  her personal tech support, she sent the discs to them to "fix" them somehow.

They played fine in my parents' set top DVD player.  My parents decided to try to make copies of them, but found that the copies would not play in their set top.

So, they called me up.  Now, since I have both my computer and XBox 360 hooked up to my TV, I haven't used my set top in years, but sure enough, the originals played in my set top unit (which is the same as my parents' Apex AD-2500 if memory serves), but any copies I made would not.  I stuck a couple other recently-burned DVD's into my Apex as well, only to find that, although they play in my PC and XBox, the set top choked on them.

So, why would the same burned DVD play in one set top player but not another?  And why would that same player choke on a copy of that DVD?  Finally, why would DVD's I've burned play on my PC and XBox, but not the set top unit?

Because you touch yourself at night

PAL?

You're not my pal, buddy

You're not my buddy, honey.

You're not my honey, babe

You're not my babe, smoochiekins

You are the samefag, failfag.

>>8
Wrong I only posted >>4 and >>6