Hi,
So are you saying the DVD does not play in your AD-L528 anymore, but it used to? Seems odd. Is the disc clean and no scratches?
It is well known that not all DVD players will play all media.
I have some DVD's I burned a while ago, that do not work correctly on my parents Toshiba player. One of them it even ejects back out saying bad disk! They all play fine on my Pioneer, in fact, it's played everything I've ever thrown at it.
The meda you use plays a big part, and many say that meda made by Ritek is one of the best.
Goto
http://www.blankdiscshop.co.uk/ and look for disks that the ADVDINFO: is something like .RITEKG..XX where XX is a number, usually 03 or 04 these days.