mobile safari download plugins - cant download mp4

hi
i have installed on my pc a software called Easy File Sharing Web Server

its an application that let me access my files from the web

so what i tried to do is to access my web site throw my iphone and download files like mp3 and mp4

i can download mp3 with my iphone with no problem
but when i try to download mp4 i get an error message that say "safari cant download this file" or something like that

but when i download mp4 from other sites, its let me download
anyone have an idea what cold be the problem?