I can not upload alarge .zip file

[thinktodo]

there is a attachment.
I have set upload_max_filesize = 50M in php.ini,and restart apache(service httpd restart),
but,when I upload a .zip file(13.8M),clicking submit button,the page jump to login page.
I notice that,there is a hint on foot:The maximum size of one file is restricted by net2ftp to 48828.125 kB and by PHP to 2M .
that,upload_max_filesize never effective.
if I upload a small .zip file,it is ok
anyone could help me?
thanks a lot