i take it that these issues appear when you're trying to access the files (from the applications) directly on the DVD.
can you copy (dragNdrop) the files in explorer to your hard drive? if so, can you then use them (with the applications etc) OK?
if so, i suggest you copy them to your hard drive, and put it off to a bad DVD.
maybe there's some issues with the Roxio software...?
re-reading your post, you say you can extract the files with IsoBuster but the extracted files are still messed up...
don't know what to say
. again, must be a bad disc, i don't know what else you can do to recover the files...
maybe some expert will have better suggestions.
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them
In the land of Mordor, where the Shadows lie
M.C. Escher - Reptilien