i've burned more than 10000 cd's as mac + pc hybrid data cd's with toast 4, 5, 6 and 7 and never had problems till today. My clients complains that they can't read my data on a pc no more. So i made several test and in fact i can't read everything on a pc. At the first level of the cd everything is fine, but i can't open or copy a folder at this level. I burned the same data on my mac with os x 10.4.6 "burn it" and surprise: everything works perfect... Does someone know where the trick is?

That seems a little strange. I guess I would just play around with things to see what can possibly be the problem
1) Try other media
2) If possible try another drive
3) Try a plain ISO-9660 disc
4) Oh, make sure you have the latest Toast updates (I believe 7.0.2).

thanks for your try... i allready did all this things. i have 6 macs and the same problem everywere. and it goes more strange: when i burn the same files as ISO-9660 disc the quark file becomes unreadable, even for all my macs???.:"!

Make sure you are using extension suffixes on the files when creaing pc and ISO-9660 files otherwise you can run into problems, even reading back on a mac.
Can the macs open the quark files from the open dialogue box from within quark?