Problem with data DVD burning across Win 7 / XP

Recently I've had a few clients complain that discs of photos I've burnt for them don't work on their PC's.

Up until about 6 months ago I never had a problem.

I've done some tests and found the following.

9/10 the disc that was burnt using native win 7 dvd burning software to create a mastered DVD won't read on my xp laptop, but will read on both my desktop and win 7 laptop.

It maybe that the player in my XP laptop is old, but that would mean I've now got a load of clients with old laptops  

But, that laptop will handle 'proper' discs just fine.
Stick an win 7 authored DVD in the XP laptop and you get that shuffle sound as it tries to read the disc. Stick it in my desktop/ Win 7 laptop and it's just fine.

Normally I'd pass it off as just an old laptop, but now the last two discs I've sent out to clients (after checking on my desktop they burnt) have been, for the client, unreadable.

Any ideas?