DVD cannot read large amount of files !!!!!!!!?

[Panda]

Hello ,
I bought 25 DVD-R, the problem i have with reading large amount of space in disk

lets say i burn 25 MB on the DVD :
1-i can read from dvd
2-i can write to dvd

but lets say i want to burn 500 MB then:

1-i can write on the dvd
2-i cannot read from the dvd,WHY ??????


with thanks
***(i used ,Nero,power2go,windows default burner and nothing work)

 

[MikeRonson]

the files too big, there not enough space on the dvd to burn....what more do you want