Some movies cant be burned??

dvdfab platinum is pretty sweet, how come it sometimes asks for a dual layer disc sometimes??

if its over 4700mb
then i need a dual layer dvdr?

 

set it to burn to a dvd-5

 

it was set to a dvd5, but the dvd i put in has like 6300

and dvd 5 only holds 4700


im trying the "split" option

 

can somone give me the split guide, i tried to burn 2 movies splitting but its all messed up and wont play



thanks again