Downlaoding problem.....

Hi there,
I have installed phpAlbum successfully, but I have problem and question.
My problem is:
- I upload certain files, each single file's size around 13MB-17MB. when some try to download them, it stopped downloaded after 3MB. I am not sure what is the problem, is it a configuration in phpAlbum or what?
My question is:
- How I can limit the access on a certain files. i.e. how can allow only specific user can see some of the photos?